We all know that in an Alternate History or Alternate Universe, tiny changes ("For Want of a Nail, the shoe was lost...") can lead to massive changes, where everything is different.
Or, as it may be, not. Sometimes what's different in the new history is less interesting than what has stayed exactly the same.
Consider how a person's DNA is the result of an ovum and one of countless spermatozoa competing to get at it. The slightest change in timing by seconds would result in a completely different person; different sex, possibly different personality and different abilities, etc. (i.e., the difference between fraternal twins). This is never addressed. Well, hardly ever.
An alternate universe could arise where the human race never developed money and society is radically different, but you'll find that you were still born, still live in the same house, and still have that tattered old E.T. doll sitting on the mantlepiece.
In an ongoing series, there's generally an element of the production team wanting to get the most out of actors and sets that they've already paid for. In both series and standalone works, the writer may be trying to draw interesting parallels between two different versions of the same character or situation, or to help impress upon the reader how things are different by showing them a familiar figure in slightly different circumstances; Richard Nixon the Used Car Salesman allows the reader to see how the world is different, rather than Richard Nixon The Person Who Never Existed Because A Different Spermatozoön Fertilized His Mother's Egg.
If the new history is the result of Time Travel, it might be possible to explain the non-changes as reality avoiding a Temporal Paradox (by making sure that there's still a time machine and a time traveller to go back and create the new history). Often it isn't. And even when it is, the writer usually doesn't bother. The other possible explanation could be that there is some form of higher power (like God, for example) preventing the timeline from changing too drastically. Another still would be the idea of chaos theory and the butterfly effect as being unpredictable in relation to its consequences. As the saying goes, the more things change, the more they stay the same.
(Note that this doesn't really apply to alternate histories where the change was something the protagonists or their parents did or didn't do. You wouldn't expect universal change within one generation.)
Of course, why does Hitler have to be the only detail history refused to change?
Compare Ontological Inertia. If we're expected to believe things "just happen" to be the same, a subtrope of Contrived Coincidence. See also The Stations of the Canon, Sliding Scale of Alternate History Plausibility and Richard Nixon the Used Car Salesman. See also Different World, Different Movies
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Anime and Manga
Near the end of the 2003 anime version of Fullmetal Alchemist, it is discovered that the alchemist world is an alternate history of ours that branched at least 400 years ago with the discovery of alchemy. In spite of this, The Movie shows several of the characters also exist in "our world," though with different histories and motivations.
Code Geass: Word of God says the alternate history goes back as far as 55 BC, when Julius Caesar's attempt to invade Britain is thwarted by the election of a "super-leader"note Although even without such a thing in real life, it still failed. — the Celtic King Eowyn, who is the first member of the Britannian royal line (this is later made year 1 of the a.t.b., Ascension Throne Britannia, calendar). The American Revolution failed. Napoleon beat the British, who then re-headquartered their Empire in North America. In the 21st century, the "Holy Britannian Empire" conquers Japan with Humongous Mecha... and yet there are still Pizza Huts everywhere.
Not to mention, if Britannia is descended from the Celts, they shouldn't even be speaking English. Or what we think of as English, anyways.
It's pointed out, however, that a good chunk of Britannia's official history was actually fabricated.
Specifically, history happened basically the same up until Elizabeth I bore a child, which did not happen in history, either by two people that existed in history, or by the "Duke of Britannia", leading to a "golden age" of the Tudors. Another 250 years later, Elizabeth III dies childless, and appoints a different Duke of Britannia as her successor.
Though I'm not entirely certain why a Golden Age of the Tudors was even necessary. Couldn't the Britannian Emperor be the descendent of Elizabeth I? Especially considering they simply did the same thing all over again, except for taking place after the American Revolution fails.
At the very least, this new Emperor Britannia, or one of his successors, retroactively named themselves part of a long line of Emperors of a nation that did not exist until relatively recently.
In the first Doraemon manga, Nobita's great grandson explains to him that even though the future will be changed he will still exist, despite the fact Nobita marries Shizuka instead of Jaiko.
Read or Die takes place in a history where the British Empire remains the most powerful force on Earth and cloning is a viable science, yet George W. Bush is still the (at the time) President of the United States, and Stephen King still wrote Misery. Some or all of this may be a result of Gentleman screwing with the Book of Truth.
It's even suggested that Reinforce does not have long to live in spite of surviving what would have been her Heroic Sacrifice. She and Hayate both know this, but don't say anything about it.
Katanagatari ends this way. Despite Shikizaki Kiki's attempts to Screw Destiny with the Deviant Blades created via methods from the future, history managed to correct itself. This is because the people he intended on carrying out his plans, his descendant and his ultimate creation, simply refused to play their part.
A major frustration to Homura Akemi in Puella Magi Madoka Magica; no matter what she does in her indeterminate number of attempts to rewind the events of the series and start them over differently, the outcome is always the same. She refers to it herself as an "endless maze".
As well as the finale; Madoka's wish Ret Cons all witches out of existence, meaning every death at the hands of a witch (Magical GirlorMuggle) didn't happen, saving countless numbers of lives who could then do more things and impact the world. Needless to say, this should radically change the course of human history, as witches and magical girls had been shown to have been around for hundreds of years... yet Mitakihara, at least, looks more or less the same.
Psyren: After seeing the wreck that the world will be in just 10 years and learning that the catalysts leading to those events will occur much sooner, Ageha and friends quickly begin investigating said future in an attempt to reverse the damage in the present. While their efforts do bear fruit ( letting some previously-doomed friends survive to form La Résistance), they realize that it will take far more drastic changes to prevent the apocalypse than simply altering a few of the particulars. Also, the biggest catalyst is the arrival of an Eldritch Abomination from outer space. ...yeah, that'll take some effort.
Most Comic BookElseworlds suggest that, whatever else happens, the superheroes still exist (unless the absence of a given hero is The Difference). Particularly obvious in many of Marvel Comics's Exiles storylines; in one the entire world has been under the control of Skrulls for the last century, humans have no access to technology, but apparently Peter Parker was still bitten by a radioactive spider.
It is actually stated, in an issue of Exiles, by the character Morph, in one of the early issues, that he has noticed that a key component missing on a lot of the worlds is the presence of the Norse Gods (Thor, Loki, Odin, etc). He then goes on to say that he thinks that if the Norse Gods were present many of the worlds would have turned out much more positively.
This one is probably best handled in Marvel Comics's Marvel 1602. In this case, a foreign element (namely, Captain America being sent backwards in time) has messed up history; the universe reacts, and "a season has dawned over three hundred years early: a season of heroes and marvels." Or more accurately, "heroes and Marvels."
In a way, 1602 actually justifies the fact of certain things and people existing in alternate universes, no matter how different — in essence, 1602 basically explains that certain people and events were destined to exist, so that altering the past may change some things, but the "important" stuff is still going to happen. Or, to put it another way, the universe itself does its best to insure that a Spider-Man, Fantastic Four, Captain America, etc. exist, no matter what it has to do to make that happen. (If by "the universe", we mean "the Marvel writers and editors.")
And thenSpider-Man 1602 has the dinosaurs die out, the accord between the Roanokians and the natives get broken, and the superhumans apparently disappear from history, so that by the time World War II comes round, the only difference between this universe and Earth-616 is that a vial of Peter Parquagh's blood is used for Captain America's Super Serum. (This may also mean it's a Stable Time Loop.)
In a special story written for the 500th issue of Detective Comics,Batman is offered the chance to save Bruce Wayne's parents in an alternate universe, knowing that doing so could mean that world never has a Batman to protect Gotham. He does so anyway, and it is later revealed that the deed inspired the alternate Bruce to become Batman as a tribute to the costumed man who saved his parents.
This is echoed in the Crisis Crossover series Flashpoint, where there is still a Batman, but with a twist: He's really Thomas Wayne, who took up the cowl after Bruce was murdered. The Joker, by extension, is also an example: what reason other than this trope would cause philanthropist socialite Martha Wayne to respond to her son's death by turning into a psychopathic clown?
In Astro City, one of the powers of Samaritan (and his arch-enemy Infidel) is immunity to Ret Gone. Samaritan was originally sent back in time to prevent the Challenger explosion, and because of his meddling undoes his world's past, he was never born. No matter what happens to the timeline, Samaritan and Infidel will still exist. In fact, Infidel once destroyed all of space-time, and they still existed.
Another Astro City story, "The Nearness of You", averts the trope. A man is haunted by dreams of a woman that he has never met; he knows her well enough to draw her picture, yet utterly fails to track her down. A supernatural character explains to him that the woman is/was his beloved wife, erased in a time-war, and offers to erase his residual memories of her; he declines, and is told that "no one forgets".
The Don Rosa 60th anniversary Donald Duck story does this with a Wonderful Life scenario. Most everybody is miserable and worse off for Donald Duck never existing...except for Gladstone Gander, whose ridiculous luck keeps him the same well-off Smug Snake he always was.
Except that he has to care for Huey, Dewey and Louey, who under his inept parenting (mostly consisting of bending on their every whim) have become needy couch potatoes estranged from reality.
In Strontium Dog, it is explained that since time is so vast, time travellers usually only exert minor changes which smooth out over time. It takes a truly catastrophic event to alter history noticeably.
One Fantastic Four storyline espouses the same idea, with Johnny Storm explaining it as "Saving Lincoln just means that everybody will remember how Lincoln was almost assassinated, only to die of a heart attack one day later." Dr. Doom mentions that the "for want of a nail" theory of time travel is a lie spread throughout the timestream by Kang to prevent the emergence of rival time-travellors.
Bishop of the X-Men comics is a "chronal anomaly" who has been involved in so much time travel that he himself is never affected by it.
An Elseworlds story in the DC Universe, JLA: The Nail, shows what would happen if the Kents had not been out driving their truck as baby Kal-El's ship crash-landed (due to a nail puncturing one of their tires). Instead he was raised by an Amish family and thus never ventured out into the world and never became Superman. Aside from that, not much had changed. All the other heroes still existed, but the public was just more afraid and suspicious of them (cause Superman was a really nice y'know), with debates as to whether they could be trusted. Oh and Jimmy Olsen becomes evil and hatches a plan that involves giving himself Kryptonian superpowers. In the end however, evil Jimmy ends up killing the now-adult Kal-El's Amish parents, giving him the Heroic Resolve to fight and defeat him. Afterwards, he becomes Superman and moves in with the Kents (who had been offering superpowered individuals shelter).
In one Silver AgeSuperman story, Supes asked the supercomputer in his fortress to extrapolate what his life might have been like if Krypton had never exploded. The extrapolated story finally ends with an odd circumstance where this alternate Kal-El acquires super-powers and becomes Superman on Krypton. Supes and Batman turn away from the screen with just priceless expressions of astonishment.
In "What if the Fantastic Four had not gained their powers?" (v1 #36), Reed Richards properly checked the radiation shielding on his spaceship, so the Fantastic Four never get their powers. As it turns out, this has absolutely no bearing on their ability to kick Mole Man's ass.
An even more dramatic example is v1 #14, "What if Sgt. Fury and his Howling Commandos had fought World War II in Outer Space?": Thanks to the inventions of Leonardo Da Vinci, mankind has advanced technology including casual spaceflight by the 1940s, but there's still a World War II and it's still got the Howling Commandos fighting in it, complete with all the usual war-comic tropes. Fury's even still a Cigar Chomper, though you'd think that wouldn't work so well in a spacesuit.
A quick study of Marvel's What If... series will confirm that, in the multiverse of Marvel Comics, that there's only two universes in which Peter Parker doesn't ever become Spider-Man. One of them has no superhumans at all, and the other has no Peter Parker at all. In every other Marvel Universe variant, Peter Parker exists, and he will become Spider-Man at some point.
The Adventures of Barry Ween, Boy Genius used this during one time travel story. When Barry and Jeremy got stuck in the Wild West, Jeremy was worried that they might change history or cause a Time Paradox. Barry dismissed his concerns, saying that humans overestimate their own significance. He claims that they could kill everyone in the town they are currently in without affecting history one iota.
In Ex Machina, the existence of the world's first super-being has no apparent effect on world history. It isn't until The Great Machine stops the second tower being destroyed on 9/11 that anything significant changes.
In Justice Society of America #31 (Part 3 of "The Bad Seed"), Obsidian gets turned into a black egg, as part of the Fourth Reich's evil plot. After two unrelated storylines (and a crossover miniseries), #36-39 are set in a Bad Future, in which the Fourth Reich rule America. In #40, Mr Terrific of the future sends his knowledge of the Reich's plans back in time, and Mr Terrific from the end of "The Bad Seed" frees Obsidian, and the Society takes the fight to the Reich and defeats them. And then a two page coda assures us that the storylines since "The Bad Seed" happened exactly the same way, only Obsidian was also there.
female Archie: (sitting between now-male Betty and Veronica) I still can't choose!
One of the few things that remains true throughout the DCU's Multiverse is that Superman and Lex Luthor will always be enemies.
Issue 50 of W.I.T.C.H. answered the question of "What if Will never accepted the Heart of Kandrakar that day?" The answer? She'd get it a little bit later on and W.I.T.C.H. is still formed. The damn thing's persistent.
In the X-Men storyline Age of Apocalypse, where Charles Xavier died young, Magneto founded the X-Men and the supervillain Apocalypse rules much of the world, there are a whole lot of characters who were villains in the "normal" timeline but heroes in the new one, or vice versa, but darn near everybody still has the same code names, and if they're not wearing the same costume as before they've at least got the same color scheme.
Better Angels has Shane Walsh surviving the ordeal at the end of Season 2 ofThe Walking Dead. He takes over Rick's position as leader, corrupting the group with his ruthless survival philosophy. Despite this, the Atlanta group is still put on a path to The Prison where Rick leads them in canon.
Zig Zagged because Shane's leadership puts the group at much worse odds than their canon counterparts.
Played with in the Star Wars fanfic Riding the Wheel of If, where in some alternate universes characters don't exist, and others even have them change gender. On the other hand, those versions of the characters that are the same gender are pretty much identical physically, and they're always the same age (per Word of God; when one author wrote a story where Obi-Wan was younger the original author said that didn't happen and it was considered AU to the series). And certain events take place in most or all universes, and if Obi-Wan and Qui-Gon both exist they're usually together, but that's all just Because Destiny Says So.
For Want of a Nail is extremely common in NarutoFan Fiction, but no matter what that nail might be, Team 7 or just Naruto himself has about a 90-95% chance of ending up in the Land of Waves and meeting Zabuza and Haku around when it chronologically happened in canon.
However, an increasingly common trend seems to be that Zabuza and Haku (or at least Haku) survive and join Konoha's forces.
Even more recently, there's been a pretty strong backlash against this, sending the protagonist team elsewhere. Oddly, these almost never actually send someone else to deal with the situation in Wave, and the whole thing is never commented on.
90% of the time Naruto learns Shadow Clone Jutsu and Rasengan no matter what happens, although since these two skills make up his entire move set it's justified.
The Naruto / One Piece crossover fanfic Shinobi Of The High Seas take In Spite of a Nail to ridiculous extremes. Despite Naruto being there and regularly interacting with the Straw Hats (including adding Nami and Robin to his harem), every major event of the anime/manga happens without fail, even if he's there. It's to the point he completely misses the entire Marineford arc, only hearing of it second-hand.
In most fanfics where Naruto grew up outside Konoha he'll almost always meets his would've been team mates in the same way: In the beginning of the Chunin exams arc while Kankuro was threatening Konohamaru despite the fact that without team 7 or Konohamaru knowing him till then the situation wouldn't have happened.
This happens in a number of ITV region "what if" tv mocks. In some, Carlton and Granada never get hold of the London and North West regions respectively, yet they manage to buy out the regions they purchased in our world and ITV is rendered to its consolidated state in 2003.
The Sonic the Hedgehog fanfic A Rose And A Thorn 4 features a character going back in time to save the Ark. Despite knowing everything that can happen, she still cannot stop the destruction of the Ark or the death of Maria. It all happens anyway, so Sonic Adventure 2 happens anyway.
Ranma ½ fanfiction will unfailingly reproduce the first six volumes of the manga, despite Ranma having been born female, travelling with his Rogues Gallery as frienemies, having acquired a different curse, having not actually gone on the training trip, having learned god-smackingly-powerful magic instead of Martial Arts and Crafts, et al.
Shinji And Warhammer 40 K is an inversion of this... it isn't the Fanfic that needed the nail, it was Canon. Still plays the first several angels almost completely to canon (with minor changes in character attitudes and relationships and much greater levels of awesomeness) but at about chapter 15 to 20, depending on the reader, it suddenly stops being anything close to canon. Probabably best summed up with the line
Shinji: Then hear my command. Send the assassins. Plant the evidence. All the things we talked about before...let it be done...Begin The Purge. Protect my city.
Very common in Harry Potter fan fiction that changes what happened the night Voldemort tried to kill Harry Potter. Sometimes Voldemort is somehow defeated despite Lily not dying. Sometimes Voldemort isn't defeated at all. Harry will still usually be the "Boy Who Lived", even if his mother, father, and twin sister also survived. Regardless, everything else that happened before the fic begins will be exactly the same, even if Voldemort should still be waging war against the wizarding community.
Another notoriously common one is that, if the Triwizard Tournament takes place, no matter what else is different, the graveyard scene will still happen, and Cedric will almost always die. Considering the sheer unlikelihood of Cedric and Harry reaching the Cup at the same time, THEN deciding to touch the Cup at the same time (and even if they do, the chances of Cedric being outright killed aren't that high), the fact that this happens without fail is more than a little jarring.
In "A Different Dursley Family", it's said Vernon and Petunia were destined lovers. The "nail" of this fic was Vernon trying to steal a statue from Smeltings (his secondary school) for a prank. In that fic, Vernon was caught and expelled for this, which resulted on him being cut from his father's will and becoming a mechanic to earn a living. This prevented him from being the intolerant man who'd force Harry Potter into Cinderella Circumstances and yet, he and Petunia met, fell in love and had a child. Prior to the fic's proper beginning, the author briefly mentioned other alternative timelines coming from the statue prank and the only one specifically stating Vernon wouldn't marry Petunia was one where the statue fell on him, causing his death. And even then Harry's life wouldn't be different from canon since Petunia would marry a squib who was so envious of his magical relations as Petunia was of her sister.
Just about any fanfic that tries to insert an Original Character, but keep to canon. The new character might steal a few scenes from others, and may replace someone as the author's favorite character's love interest, but don't expect anything important to actually change because of this character's existence.
In the Pony POV Series, despite unforeseen circumstances like the Windigos, Discord's first reign, and Nightmare Moon, the version of Ponyville designed by the Alicorns and Draconequi during the Cosmic Retcon of G3 still comes into existence as planned.
Oh, god — the gradually broadening, world-engulfing trope that is OmegaVerse. A human culture that had normal male and female "betas", powerful "alphas" that whether they appear as male or female can impregnate, and "omegas" that whether they appear as male or female undergo periodic sexual "heats" during which they can be impregnated — and during which they are irresistibly attracted to any alpha within scent range, said alpha inevitably reciprocating — would not be in any conceivable way the same as ours. Not remotely.
In Perfection Is Overrated, while the SUEs' arrival results in an alternate suspect arising for the attack on Yukariko, resulting in the Himes not going after Nao, there are several other changes. Yukariko and Ishigami die when Ishigami tries to take advantage of SUEs with the ability to alter their targets' memories and personalities to spark infighting among the Himes. The First District still gets destroyed, not by Shizuru, but by The Usurper-possessed Obsidian Lord, a brainwashed Mikoto, Nagi and two SUEs.
The Infinite Loops have this hardcoded into their premise. An anchor is intended to stabilize a universe, no matter how many variant loops it goes through.
Pretty much the whole point of the For Better or for WorseFixFic Foobar; try as Elly might to use magic to make her future better, her very limited ability to influence events (and ignorance of the fact that her victims are aware of what she's trying to do) result in only a minor change in her surroundings. Said minor change is a true awareness of how damaged she is.
In Dauntless, the "Nail" is Clovis discovering Lelouch is alive, reuniting him with the Britannian royal family. Though a lot of things do change, Lelouch still makes contact with C.C. and still gets his Geass.
Despite the Britannian Empire not being a thing in the world of Justice Society of Japan, Lelouch is still Zero, he still works with C.C., he still has a Geass, and he's still the head of a mercenary company known as the Black Knights. The reasons for this are, as of now, unknown.
To Paragon!John Shepard's shock, when he meets his Renegade!Female counterpart in Mass Effect: Life is a Game, Jane says that she killed Wrex, Mordin and Legion in her first playthrough. Except, despite her joking about it, there is absolutely no way she'd promote Uldina to the Council over Anderson, something she and John are in complete agreement about.
The fact that the divergent Paragon and Renegade paths both inevitably led to them facing down the Star Child in the same way at the same time really ticks her off.
In Façade, despite the fact that Yu Narukami is female, the plot chugs on as usual as far as events go. Thus far at least, Yu's budding friendship with Mitsuo might change things...
White Mans Burden is set in a world in which black and white people have switched cultural roles, but besides that, 1990s America is still pretty much the same.
Terminator 3 shows us that no matter what, Judgment Day will still transpire circa the turn of the century.
In a way, the climax of Terminator 2 made things worse, since the new version of Skynet designed in Terminator 3 wasn't a supercomputer, but software which was able to infiltrate the Internet, which is decentralized and much harder to destroy.
Back to the Future is a good example — Marty accidentally prevents his parents from meeting in 1955, so has to get them together in order to protect his existence. When Marty returns to 1985, his father George is more confident, his mother Lorraine is no longer an alcoholic, his siblings are no longer dead-end losers, Biff is no longer George's supervisor, Twin Pines Mall is called Lone Pine Mall and Marty now owns a spiffy pick-up truck — but just about everything else is exactly the same. Marty and his siblings still exist and were still born on the same days, they still live in the same house, his room is exactly the same as in the "old" timeline, Marty is still dating Jennifer, and was planning the exact same trip to the lake as "before".
Except that no matter what else changes, in every reality and time (at least when the man is around), Uncle Joey is always behind bars.
When the picture of Marty and his siblings is restored, after Marty fixes the timeline, Doc reacts as though something about Marty's older brother is different than before the images faded (the restored picture is not shown to the audience). Perhaps something in the script didn't make the final cut.
Then, in Part II, you have 1985A. In this timeline, a lot more has changed: Biff becomes insanely wealthy and George gets murdered by Biff. Yet, Marty and his siblings still exist, Michael Jackson still becomes a famous pop star, and A Fistful of Dollars is still made.
George fathered the three before Biff had him killed; Lorraine even says Marty looks like his father George.
Note that Marty's 1985A siblings have apparently reverted to their original Jerkass loser personalities.
Part III had Marty embarrass Biff's Wild West ancestor and get him arrested, and Marty and Doc rob a train to drive it off a cliff. This didn't change anything at all, except that now Clayton Ravine is called Eastwood Ravine (named for Marty's alias instead of the schoolteacher who "originally" died there).
They actually discussed this in the commentary for Part II when Biff goes back from 2015, with Marty and the Doc still there. They discussed why it never changed, and decided it'd be better if things remained the same at that moment.
In the Alternate Universe of Almost Normal, in spite of homosexuals being in the majority (with heterosexuals being the ostracized minority), the culture and society seems to (otherwise) be much of the same. Brad still exists, along with everyone else he knew. It's interesting to note that the homo/hetero flip has led to changes in French history.
In the 2009 Star Trek movie, no matter what the Big Bad does, the original cast of TOS ends up on the Enterprise in the spots they filled on the show. It's implied that his actions cause the group to coalesce sooner than they did in the original timeline.
In the case of Chekov, it actually caused him to be born sooner. It's interesting to imagine that as soon as they heard the news about the destruction of the Kelvin, Chekov's parents' first reaction was "we should have sex!", and that's why Chekov is older in the new film.
This happened to Kirk as well who was born two months earlier than he should've been. Nero's arrival somehow caused Kirk's mom to go into labor (maybe intense stress or something) causing Kirk to be born in January instead of March like his original timeline counterpart. The novelization of the 2009 movie reveals that Kirk's mom had an inhibitor device to impede the pregnancy while she was still on assignment aboard the USS Kelvin. However, as soon as Nero showed up, the impact of the Narada's weapons on the ship somehow caused the device to fail.
The only other main difference is that Spock and Uhura's romance is now much more blatant and not one-sided.
And y'know, despite that they never have a history, Kirk and Khan will ALWAYS be at each other's throat, and Khan will always make one of the main cast die in a radiation-filled engine room
Though apparently a line they filmed but cut (for what reason?) had future Spock say that the timline and the universe were trying to repair themselves, hence the reason why they ended up on the same ship.
It's way bigger than that. The film shows major cultural consequences of humanity's inability to lie, such as the fact that there's never been any fiction or religion, yet all the countries seem to be the same, there was still a black plague in the thirteenth century, Napoleon still conquered half the world, Coke is still competing with Pepsi, etc.
And despite Christianity not existing in the film's universe, the calendar still ended up exactly identical to the Gregorian calendar. Think about it: how did they decide what year to mark as 1?
A Swiftly Tilting Planet by Madeline L'Engle does this AND For Want of a Nail at the same time. Charles Wallace (and a unicorn, and Meg... sort-of) need to zig-zag though time, making a dozen changes scattered throughout history, to replace a dictator poised to start World War III with a nicer near-clone. But no matter what events they change, no other effects show up in the present. And they even screw with Meg's husband's family!
In Kim Newman's Anno Dracula series the central premise is a) vampires are real, as are all fictional characters (and more of them are vampires than you'd expect), and b) Dracula vampirised Queen Victoria and ruled Britain for many years. But by the second book, World War One is happening in roughly the same way it did in ours (with a Lampshade Hanging that many believe it wouldn't have happened without the vampire influence), and by the third book (set in The Fifties) the vampires seem to have had no real effect on history at all; they exist, but everything else is the same.
The original comic-book version of The League of Extraordinary Gentlemen is set in a similar world, although this is far more obvious in all the "supplementary" material than the main action.
In Kim Newman and Eugene Byrne's Back in the USSA, American government and capitalism collapse in 1917 and Eugene Debs leads a Socialist revolution. After that things go much as in the USSR in our timeline, but with American figures — e.g., Al Capone fills the role of Stalin, J. Edgar Hoover is the equivalent of Lavrentiy Beria, and Eliot Ness is an agent of the Federal Bureau of Ideology. Dissidents risk getting exiled to Alaska.
Harry Turtledove's Timeline-191 series is notorious for this. Not only are many of the same historical figures around (albeit often in different positions), but most of the story arc is copy/pasted from the history of Germany and France in World War One and World War II including the Holocaust happening to southern blacks.
Interestingly, the original TL-191 novel, How Few Remain, largely averted this Trope. The following Great War trilogy at least made some effort at averting it as well, with notable butterflies and Expys of post-PoD historical figures... at least on the American side of the Atlantic (in Europe, however, he played it straight).
Similarly, his collaboration with Richard Dreyfuss, The Two Georges, concerning a giant British North American Dominion born of George Washington and King George III cutting a deal featured not only Governor General Sir Martin Luther King but a used steam car tycoon named "Honest Dick" in Southern California.
And again in In the Presence of Mine Enemies, in which the Nazis won World War II, he copy-pastes the fall of the Soviet Union. It's shifted forward about fifteen years, but the world's largest totalitarian government still crumbles after the appointment of a pro-glasnost Fuhrer, a right-wing coup against him, and a popular uprising with a megalomaniac, alcoholic local governor at its head, who ends up the front-runner for head of state once his state becomes its own country.
The copypasting is then taken to ludicrous extremes in The United States of Atlantis, this time with an American Revolution with only the settings changed to reflect the Alternate History geography that created the new timeline, and with an Expy substituting for George Washington.
Copy-pasting real world history is Turtledove's shtick. Timeline-191? CSA = Nazi Germany. In the Presence of Mine Enemies? Nazi Germany in decline = USSR in decline. The Man with the Iron Heart? Modern-day Iraq War.
The Man in with the Iron Heart is the worst one - basically, a Nazi-led insurgency in Germany just after World War II somehow succeeds in driving the British and Americans out. This, after fighting the largest and most destructive war in human history against them, but also with the Soviet Union just across the border - and the widely-held belief that as soon as the Allies leave, the Nazis take over again, this time with nuclear weapons!
That and the Nazis somehow are able to pull off stunts that resemble modern day terrorism's finest dreams despite having much lower levels of tech and having been completely and utterly raped and burned in ways that modern day extremists are lucky they haven't been.
Also, Heydrich's real-life assassination, the one whose failure is the PoD, wasn't just a random attack by partisans; it was planned in real life by MI6, who by that time really wanted Heydrich dead for a number of reasons, not the least that he was threatening several high-placed German double agents. It's doubtful they would have just given up after one attempt.
The war that came early begins with General Sanjurjo surviving the plane trip from Portugal in 1936 and he, not Franco, leading the nationalist forces in the Spanish Civil War. The action then jumps to 1938, at the height of the Battle of the Ebro, and the narration notes that Sanjurjo failed to take Madrid early in the war because he preferred marching on Toledo first. In reality, Toledo and the attack on the XYZ Line that made possible the Republican counterattack on the Ebro were both Franco's personal blunders for which he was criticized a lot in his own side; had Sanjurjo been in charge he'd probably acted differently.
Jonathan Strange & Mr Norrell features an Alternate History of Regency Britain where magic and The Fair Folk exist, the setting is little different than the actual Britain of the time and historical figures are exactly as in reality. Also, although magic is used in fighting the Napoleonic Wars, they still end up finishing at Waterloo with an British/Dutch/German victory.
It gets worse. For the majority of the Middle Ages, the northern part of England was ruled by a Fairy-sponsored magician-king. This has almost no appreciable effect on the timeline.
In a series of books by Vasiliy Golovachev, people with any psychic power are explicitly said to be resistant to past-altering powers. To be more exact, their personalities and memories are. Should their parents never meet, they will be born from other parents. This probably should cause a lot of confusion, as they might not know who their new parents are, and previous parents will forget them. The world once changed the sentient life in the past (sentient cockroaches to sentient apes), and there were people to witness it.
The Temeraire books by Naomi Novik are Napoleonic alternate history WITH DRAGONS! The fact that all the major world powers now have air forces has had very little effect on the course of European history, though outside Europe things seem to be considerably more different—particularly in Africa which has an empire built on dragons.
Also, starting with the timeframe of the books, the history of the Napoleonic Wars begins to diverge slightly from our own. This may be One Shot Revisionism: if European history was the same as our up until the timeframe of the books, why should it start diverging just then?
The books mention that in Eurasia, dragons are seen as little more than very large, more-or-less intelligent horses that can fly. Because most people are afraid of them, the dragons are kept away from civilization and these myths are allowed to perpetuate, and the dragons are prevented from impacting the culture. The cultures that are noted as being different are the ones that treat the dragons as the equals they really are (the Africans mentioned are actually led by dragons, and the Incan empire is still intact in the 1800s, having used dragons to drive the Spanish off).
Note also that the relationship of non-European peoples and powers to the European powers is quite different in the world of Temeraire than in ours. Here, China is a Great Power, able to make Britain walk and speak softly when dealing with it (though racist attitudes vis-a-vis Chinese still exist), the Inca have been able to hold off the Spanish for centuries, and the African empire drives the European colonists and slavers clean off the continent, with great slaughter.
As far as the Napoleonic Wars go, the campaign against Prussia in 1806 goes off pretty much as in our history, though later on Napoleon is able to launch his invasion of Britain, and does overrun much of England, although the Grande Armee is finally driven out. Furthermore, Lord Nelson survives the Battle of Trafalgar, though severely injured, although he is later killed in action in the crucial naval battle of the campaign to drive the French out of England.
As the story develops the questions and inconsistancies become greater, especially in light of how quickly the British are able to increase their numbers of dragons. With Birthrates like those, you'd think that the Dragon's would've displaced humans by now, especially as they're generally shown to be at least as intelligent.
In Diana Wynne Jones's Chrestomanci books, most of the main characters live in a universe where magic is functional, the French won the Battle of Agincourt, and North America is called "Atlantis" and is dominated by a Modern Mayincatec Empire. Nevertheless, a substantial fraction of the people there explicitly have counterparts in our world.
Lampshaded in Night Watch: "Historical Imperative", as it's called by the History Monks, ensures that a time-displaced Vimes takes the place of his teacher after said teacher's death at the hands of another time traveler so that the "present-day" Vimes will be the same as he was before the time travel incident.
The Discworld runs on Narrative Causality, which may have also had a hand in it (or be another side of the same thing as Historical Imperative...).
An alternative view, with some substantiation based on other appearances of the History Monks, is that "Historical Imperative" is shorthand for "that version of events favored by the History Monks".
Also, in the second and third The Science of Discworld books, the wizards try to avert changes in history wrought by elves and Auditors, to ensure that Shakespeare and Darwin will complete their works and the Roundworld humans will achieve space travel before the next iceball smacks into their planet. In many versions of history, Darwin writes "On The Theology Of Species": a superficially-similar treatise that describes natural selection, but blames it all on divine will, hamstringing scientific reasoning for future generations.
Not to mention that this causes Richard Dawkins to write the real Origin (as in "of Species") later, with the shown excerpt worded identically to Darwin's version.
In Mort, the title character is acting as Death when he saves a princess that's supposed to die. It turns out her sucessor, while an evil man, would have united the city-states of the Plains. At the end of the book, Mort is reminded he needs to work to ensure this happens anyway.
Averted in Small Gods, in which the main character was supposed to die. Thanks to the intervention of one of the monks tasked with keeping the timeline working, he survives, prevents a hundred years of war and the "death" of a god.
Nation by Terry Pratchett is set in an alternate universe where the geography of the Earth is different, several new species of animal exist, most of the British royal family died in a plague in the mid-nineteenth century, and over the course of the story it is discovered that an advanced civilisation arose in the Pacific islands 35,000 years ago. This fact becomes common knowledge and the subject of major scientific interest. The epilogue takes place in the present day and namechecks several real-life scientists who apparently still exist and work in the same fields.
Johnny and the Bomb has the protagonists overcome their worries about For Want of a Nail and save a couple dozen people from getting bombed. As a result a couple streets have different names and a few shops have changed, but that's about it.
The Animorphs book Elfangor's Secret opens in an alternate history where Visser Four traveled back in time and mucked with (among other things...) the American Revolution and World War II (and Agincourt, but that was because his host body constantly recitedHenry V to annoy him), trying to ensure that human society would be oppressive and backwards. He gets results, but all of the Animorphs are alive and superficially similar to their true selves — Cassie (who is African-American) owns a slave, but her usual-timeline boyfriend, Jake, still considers turning her in to the police because he wonders if her softness towards her slaves means she's liberal and opposes the Empire. Also, Blood Knight Rachel is replaced by her friend Melissa Chapman, as this society "has no use for uppity, aggressive females," and she's in a reeducation camp being taught "her place."
Not sure if this is intentional, but another book has an explanation for this. It turns out that the Ellimist made sure that those particular kids became friends and started fighting the Yeerks, no matter what the timeline.
"Hardcore" Alternate History refers to this trope as "the butterfly net" (as in the butterfly effect) and considers examples of AH works that use it to be unrealistic or frivolous — similar to the Mohs Scale of Science Fiction Hardness. Very commonly used in published AH, of course, because it's funny to see Richard Nixon as a used car salesman, even if the timeline diverged in the 1760s. Its use may, however, also be regarded as an example of Viewers Are Morons.
In ...And thunder did not struck by E. Lukin, a History Protection Group employee explains why he despises "chronobumbles" — guys who steal (very limited) time-machine, don some "authentic" cloth and jump by schoolbook and tourist map:
In Harry Harrison's Rebel In Time the bad guy is just such a chronobumble: he aims to help the South win, but fails because the history book he used doesn't mention John Brown and Harpers' Ferry.
In the Dragonlance novels — specifically the Legends trilogy, which is aimed squarely at Time Travel — the point of view is that, if you're one of the races that was created along with the universe, it doesn't matter what you do in the past, events stay pretty much the same. The underlying principle is that time essentially is like a fast-flowing river — if you throw a pebble into that river, it may cause a few tiny ripples, but these ripples will be lost in the overall flow of the stream.
If, say, a kender were to travel back in time, however...
In The Dragon Waiting by John M. Ford, Christianity never took hold in the Roman Empire, Constantinople didn't fall to the Turks, and France was partitioned between England and Byzantium sometime in the 12th century. The Wars of the Roses still seemingly happen exactly as they do in reality up through the crowning of Edward IV, with the exception of one relatively insignificant death.
The Saga of Darren Shan explains that if history is changed, then the same events happen, but the roles are just filled by different people. So when Darren goes back in time and stops himself from becoming a vampire, some other person would become a vampire in his place, some other person would take Steve's place, some other person would take Debbie's place, etc.
It does add one very unusual twist: whatever force is responsible has to proactively create the new people and ensure they fill those roles. This becomes plot-relevant due to details of an action's morality and a person's afterlife being testable in-universe. To use the Hitler example, killing Hitler wouldn't prevent any of his atrocities or their consequences in history, but Hitler himself would die without having committed any of his evil acts (or having chosen to commit some of them), and his replacement, having no free will or way to avoid doing everything Hitler "should have" done, would be personally blameless for all of them (though he or she would still be born with the innate potential to choose to be Hitler, and would probably be badly affected by living Hitler's life). This distinction drives the last hundred pages of the story, after the climax.
Christopher Stasheff's Rod Gallowglass in one of the later books, discovered that he's somehow extraordinarily "probable" — it seems there's someone with his face and character in lots and lots of universes.
The Big One series has numerous radical changes in history and international relations following on from Britain surrendering to the Nazis in 1940 — but the presidents of the United States, after FDR's death in '44, are Dewey (who beat Truman), George Patton, Curtis LeMay, Johnson, Nixon, Carter, Reagan, Bush I, Clinton, Bush II, and "Jeb" Bush in 2008. However, the key point is the subtle differences in the characters of the Presidents in question. Lyndon Johnson is equally devious but without the pressures of Vietnam is much more of the social reformer he wanted to be. Nixon is a little less paranoid, Clinton more 'Presidential'. Contrasting the TB Overse presidents with their OTL equivalents is an indication of how much the different environments has changed them.
The book What Ifs? of American History is a collection of essays by historians on what could have happened had certain pivotal events gone differently. Most of them play For Want of a Nail straight (though most of them do point out the ultimate futility of speculating on "what could have been"), such as Grover Cleveland not backing down from conflict with Britain in 1896 resulting in aversion of WWI (and presumably WWII too) thanks to America becoming a non-isolationist world power early on, but the one about what could have happened had the Japanese government called off the Pearl Harbor raid presents an outcome in which it takes America slightly longer to enter WWII - but only slightly, as the Japanese prove to still be so bitter toward America that they give the Americans their "day of infamy" in 1942 anyway, and the Axis powers are still defeated in the end, complete with two atomic bombings on Japan.
Notably averted by the Wheel of Time series, which is kind of odd in a series in which destiny is so important. In the second book we get a glimpse of dozens of timelines: several alternate ways the life of The Chosen One could have gone, plus one timeline in which humanity has been extinct (or so it appears, at least) for hundreds of years. The main character could have died young, could have Jumped at the Call instead of running from it, could have been an Evil Overlord, and probably was never born at all in some timelines (or at least, was not born within centuries of when the character we know was born), and it's safe to say that the same is true of most if not all other characters as well.
One detail remains true in all alternate possibilities of the Chosen One's life, however. In each and every life he could have lived, sheepherder or slave, farmer or warrior or madman, he never gives up against the Shadow.
In Esther Friesner's Druid's Blood, magic works, so powerfully that the Druids stopped the Roman invasion and (presumably) any later invasions and kept Britain Celtic, but by the 19th Century London and the British look pretty much the same apart from details - teleported scrolls instead of telegrams, Beltane fires in Trafalgar Square (they did fight Napoleon, he was a Gaulish Druid), Queen Victoria as a witch, etc. But this is strictly Rule of Funny, since the point is to set a Sherlock Holmes adventure in a Celtic fantasy world.
In the short story "The Haldenmor Fugue", from the Doctor Who Storybook 2010, the Doctor teams up with a 21st century woman called Carla to stop temporal incursions in her home city of Haldenmor. The result is that Haldenmor was a minor Viking settlement in the 10th century, and then disappeared from history. Nonetheless the Doctor tracks Carla down. It takes some doing, because in the new history "her ancestors moved to Brazil in 1600". What, all of them?
Isaac Asimov's novel The End of Eternity has an organisation that exits outside of time, in a location called "Eternity", from which they effect changes on "Reality". It is stated that even for major changes, the effects die away after some centuries; thus all changes are pretty much local.
The grand daddy of them all: A Sound of Thunder - the characters go back more than 65 million years, step on a butterfly and the changes roll down through the ages until they get back and the only apparent difference is that no one can spell and a fascist was elected President, thus implying that 1) the human race still evolved in exactly the same way, 2) humans still speak English, 3) the presidential candidates of the most recent election were still born and still chose to run for President, 4) in what is still the United States.
The Time Machine gamebook series does this in a weird way. The rules of time travel strictly forbid the player from changing history, for example by killing people or animals... but the plot of the books tends to involve the player saving lives of several people who would die without his intervention. Somehow this apparently doesn't affect history.
"How Much Shall We Bet?" from Calvino's Cosmicomics has two characters from the beginning of time betting against each other on the events of the universe, and the viewpoint character starts making specific bets about human events back when the two were still betting on whether star matter would condense into solid, orbiting objects (such as betting that the Assyrians would invade Mesopotamia before there were Assyrians, Mesopotamia, Earth, or even a certain G-Type yellow star that would eventually be the center of the solar system). Despite starting to lose his bets more and more frequently, the situation of his bets still occurred millions and billions of years after he predicted them (a man got three years imprisonment instead of life for killing his wife, a certain illegally constructed building was nine stories instead of twelve). Somehow, though each of his bets seemingly rested on the basis of billions and trillions and quintillions of previous precise predictions, the events of the bets still developed the exact context needed for him to lose (an almost infinitely higher probability than the context never forming in the first place).
Though George W. Bush's presidency and his policies never occurred in Dale Brown's books, the US of 2012 is somehow still recovering from a major recession.
In L Jagi Lamplighter's The Unexpected Enlightment of Rachel Griffin, monotheism was a slight historical curiosity, adhered to by a minor group in ancient history the Israelites, but world history managed to trundle on without it. The Holocaust happened on schedule, being framed as the mass murder of Gypsies in this world. note In real life, the gypsies were indeed targeted by the Holocaust. May be justified in later volumes, in that we are given plenty of clues that history was forced onto this track; those responsible may also be keeping the sequence of events the same.
Especially the one where everything was exactly the same except that women had moustaches, and the one where the sky was purple but things were much the same until the Robot War.
In Star Trek's "Mirror, Mirror", Kirk visits an Alternate Universe where the Federation of Planets is a repressive interstellar empire — but there's still a starship Enterprise, and it has mostly the same crew (although not all of them perform the same functions).
Likewise for the sequels in the various spin-off series. This is despite the characters from the "original" universe causing changes that kill off or radically change various of their counterparts; the Alternate Universe is still directly alternate.
Similarly, in the Star Trek: The Next Generation episode "Yesterday's Enterprise", history changing so that the Federation has been at war with the Klingons for the past twenty years has no apparent effect on the Enterprise's command roster except for the absence of Worf and Troi and the survival of Tasha Yar. It does affect the rest of the ship's compliment, though, as instead of nominally carrying 1,014 in Starfleet personnel, civilian crews, families, and passengers, it was a militarized ship capable of carrying 6,000 troops, and the only observed civilian on board was Guinan. (Wesley was still there, but as a fully-commissioned officer, when his "main" counterpart was still an acting ensign.)
Lampshaded in the TNG episode "Tapestry". Picard becoming a paper-pusher assistant astrophysics officer instead of a legendary starship captain had no apparent effect on the rest of the crew roster, yet that was because of Q's promise to Picard that anything he does in the past will not affect anyone else in the present.
The episode, "Parallels," has Worf going through several dimensions, and while Enterprise remains mostly the same, the changes keep mounting to the point where Wesley was the tactical officer, Picard died during the events of a "Best of Both Worlds" (leaving Riker as Captain), and Troi had married Worf. They also ran into a Riker from a universe where the Borg had conquered the galaxy.
In Deep Space Nine, the Mirror Universe has the station inhabited with largely the same characters, even if some of them are there for vastly different reasons; such as O'Brien, who is (strangely) virtually the same as normal O'Brien (and not, like almost everyone else, evil), and is only on Deep Space Nine as a slave.
And yet a later episode explicitly stated that Jake Sisko was never born there. So any future descendants of Jake will not have counterparts there either.
The most baffling thing is that Vic is still on the station — but isn't a hologram.
The trope is shortly averted: over the course of three or four Mirror Universe episodes, several major and minor alternates die onscreen or off, including Ben Sisko, Jennifer Sisko, Odo, Quark, Rom, Nog, and Vic Fontaine.
Spin-off fiction takes it further; there are Terran Resistance cells equivalent to the Voyager crew (including Neelix and Kes!), the Stargazer crew, the Excalibur crew, the Titan crew, etc. And they fight Alliance members who are counterparts of the aliens in the same crews.
Some of the universes in the Star Trek: Myriad Universes spin-offs are even worse than the Mirror Universe. If Khan Noonien Singh won the Eugenics War, and humanity spent the next four hundred years being genetically engineered and only breeding according to strict eugenic principles, it beggars belief that the Deep Space Nine cast even exist, let alone are patrolling Bajoran space in a ship called the Defiance.
Christopher L. Bennett's Myriad Universes novella Place of Exile proposes that the characters are linked to their alternate universe counterparts though subspace. In his annotations he says "the physical connection across different timelines means that there can be a sort of quantum resonance: the shared 'inertia' of different quantum facets of the same being causes their lives — and their genetics — to develop along similar lines."
Then there's a less extreme example in The Animated Series episode "Yesteryear", in which Spock died at the age of seven because he failed to go back in time to save his own life. Nothing changes on the Enterprise except that the first officer is an Andorian we've never met before. Everyone we know but Spock is still alive, in the same positions, and they are still on the same assignment.
A Myriad Universes story explores the alternate universe in more detail and follows the life of said Andorian. There's no major difference in the timelines until the events of Star Trek II, at which point divergences begin to happen almost exponentially.
This trope is explicit in Farscape. First mentioned in "Different Destinations...", when Harvey tells Crichton that "If nudged closely enough to course, events have a way of restructuring themselves. If the participants are the same, the venue's the same, the motivation's the same, then, well, the outcome is likely to be the same." It's confirmed by the Ancient "Einstein", and soon put to use again when the crew has to fix Crichton's past.
In Inferno, the Doctor borrows power from the Inferno Project to jump-start the TARDIS and winds up in an Alternate History where Britain has been a fascist dictatorship for decades — but there's still an Inferno Project (though the alternate versions are closer to completing their project), run for the same purpose by the same people (although, again, not always in the same roles). Which is convenient, since he needs to borrow power from them again to get back home.
In "Father's Day", Rose remembers her father, who died alone in a hit-and-run accident when she was a baby. She goes back in time and saves his life instead. This creates a Temporal Paradox and prompts the Clock Roaches to start eating people. Her father ends up setting things right by throwing himself in front of the car that was supposed to have killed him, but this time Rose is there and comforts him while his life slips away, thus altering her own past in a trivial way that doesn't affect the greater march of time.
In "Rise of the Cybermen", the Doctor, Rose, and Mickey visit an Alternate Universe where history is different enough that Britain has a black President (yes, president) and a thriving zeppelin industry — but Mickey was still born and lives at the same address (though he's named "Ricky" and implied to be gay, and his grandmother is still alive). Both of Rose's parents also exist in this universe under the same names, and were still married, although Rose herself was explicitly never born and Pete never died in the eighties. There doesn't appear to be a Doctor, though, or he's seriously shirking his world-saving duties. Until the series 4 finale, that is.
In "The Waters of Mars", this takes a darker turn as the Doctor attempts to break the laws of Time in order to save someone that history says should have died. Despite his efforts, or rather because of them, she commits suicide, and history is altered but still preserves the key elements that cause the future to occur as it should.
Which, given how bloodthirsty the Sovereign was, kinda makes you wonder why people in "our" world weren't dropping dead left and right as he cut down their doppelgangers.
It was also later discovered that if you were in the limbo-like realm which connected the two worlds when your counterpart died, you would not be affected. This was how the AU Iolaus was able to survive his counterpart's death and how Hercules was able to survive the Sovereign's death in later episodes.
'Misfits'' had an episode where the Nazis won World War II. The characters looked exactly the same, and despite never knowing each other before the events of the series, they had met each other.
In Journeyman, the lead character of Dan Vassar, while traveling through time, meets and interacts with his friends and family in the past. This never has any impact on the present day and it seems no ever asks the Dan in their time about something the time-traveling Dan mentioned to them.
Of course, the "no changes in the present day" part could just mean that it's a Stable Time Loop.
In the next to last episode, Dan accidentally makes a change which replaces his son by a daughter, and advances technology to boot. This seemingly averts the trope, because changing the time of someone's conception did have an effect. Yet such a drastic personal and societal change didn't stop him from having the same people visiting him on the same date, his brother getting his girlfriend pregnant at the same time, him having a picture of himself meeting a scientist on the same day, etc. He even meets a psychic in the changed history, and a direct follow-on to that meeting in the fixed history with no indication that things have changed in any way. And the history with the daughter clearly wasn't a Stable Time Loop, either.
Rubberband History. It's stated pretty explicitly that there is some sort of intelligence guiding the "Journeys," and that is what keeps everything nearly identical. Likewise, Dan's son becoming a daughter was used because otherwise, what reason would he have to undo the massive technology jump he caused?
In the Stargate SG-1 two-part episode "Moebius", the team muddles around with Egypt 5,000 years ago. Their admittedly small changes result in a world where the Stargate hasn't been discovered and the main characters aren't quite as cool. Those characters go back and fix things, which results in everything being the way it was before, with the exception of a pond that was but now is no longer devoid of fish (and the sudden existence of a certain lieutenant colonel)...
Which should suggest at least some differences with O'Neill's personality as he doesn't like fish getting in the way of his fishing and therefore probably wouldn't have bought a house with a pond with fish in it, but this is ignored.
And they have a ZPM, which was actually the whole reason they went back in the first place if I recall.
This is apparently how the world works in LOST, with one character explicitly stating that "the universe has a way of course-correcting" to make sure that changes to the past don't have any major effects.
Although this could be wrong, as we've never seen anything that couldn't be explained as a 100% Stable Time Loop with regard to the actual time traveling. Even an apparent change to Daniel's journal in the past was explained when we learned about his memory problems. Desmond's future flashes, however, do allow him to change the future, but then apparently fate course-corrects back.
Red Dwarfhand waved this in one episode by specifically erasing two characters from history, yet having the two characters still running around trying to not be killed by the guy who erased them. They run into the main characters and find that their "twins" are slightly off and played by completely different people, like the "fraternal brothers" thing only even more distinct than that. Yet the ship still exists and the accident still happened and Dave Lister still managed to be frozen in stasis for three million years, etc.
Red Dwarf was a repeat offender. The 3rd season episode "Timeslides" had Dave Lister changing history so that he became a millionaire and never left Earth, prompting the Cat and Kryten to vanish from existence ... yet, bizarrely, Rimmer (who was only revived as a companion for Lister) is still stuck on the ship, 3 million years into deep space. Likewise, 7th season episode "Tikka to Ride" has the crew accidentally avert the assassination of John F Kennedy, which results in a Crapsack World future where the US space program, and hence Red Dwarf, never existed ... yet, bizarrely, the crew and their time machine aren't similarly erased from existence. Then there's ... you know what? It's probably best not to think about it.
Especially when you realize that Lister's children from his one-night stand with his own alternate universe female version were written out even though future echoes implied they'd be on Red Dwarf for decades, not to mention the fact that Lister effectively creates an ontological paradox where he becomes his own father (or, more accurately, has always been his own father). Time travel in the Red Dwarf universe is insaneat best.
Mud, a BBC live action children's series from the 1990s, ended with the characters returning from a trip back in time and accidentally bringing Christopher Columbus home with them. They go home and everything seems normal, until they try to watch Baywatch — which their mother has never heard of, because the discovery of the Americas must have played out somewhat differently due to his absence. If this was supposed to be a Sequel Hook it fell rather flat, and the viewer is Left Hanging as to whether or not they manage to sort it all out.
The Sarah Jane Adventures episode "The Temptation of Sarah Jane" claims that when history gets "diverted", it tries to correct itself, explaining why, in a world enslaved by the Trickster since 1951, Rani's mum still exists and they "happen" to run into her.
In the 1st series finale to Primeval, a change in the Permian era, i.e. over a quarter of a billion years ago, erases Claudia from existence whilst leaving the rest of the team untouched down to the clothes they are wearing and Stephen still remembering having had an affair with Helen.
In season 2 we find out the full extent of the changes: the team has a new base, also Claudia isn't really gone, she just has a different name and personality. This is despite Professor Cutter repeatedly stating that screwing around with history has sent evolution down a completely different path.
This issue is actually given as a reason why everyone thinks Professor Cutter has just gone a bit nuts instead of history actually being changed. His response is that there could be many more changes he doesn't even know about.
Which makes sense, because only memories and records of her were inserted "retroactively" — she herself wasn't. Her history was created to dovetail into what had already happened, so of course she did nothing to change things. It may also be the case that the Scoobies' memories were altered such that they remember Dawn playing an occasional role in making things turn out the way they did. It would be interesting, for example, to find out just what they remember of Dawn's involvement in That Certain Halloween.
This is covered in the comic collection False Memories (June 2002), where we see some events of the past seasons from Dawn's perspective. She also appears in comics from 2003-2004 set before "Welcome to the Hellmouth".
Considering that Dawn would have been a quite young child during the early series, and that Buffy was trying to keep her separate from any Slayer-related activity even when she was 14 and beyond, it's no surprise that she had no influence to much of the plot.
In the alternate Wishverse, Giles somehow got to Sunnydale despite Buffy's not being there and Giles not knowing that Buffy was supposed to be there, even though his sole reason for coming to the town in the normal timeline was to find Buffy and become her mentor. Cordelia questions this, but is killed before we can get an explanation.
Less bothersome with the other characters, because they all lived in Sunnydale independently of Buffy, and the divergence point was only about three years earlier. Which brings up an interesting general rule: The further back in time the divergence point is, the weirder In Spite of a Nail becomes.
Babylon 5: In "War Without End", we see the Ivanova of a timeline where Sinclair and Babylon 4 never went back in time recording a message before Babylon 5 blows up. She's wearing the uniform that Delenn had made for her. But in this timeline, because Sinclair didn't go to the past, Delenn wouldn't have been born, because she's Sinclair's descendant.
The 4th season of Eureka plays havoc with this trope. Five of the main characters accidentally travel to 1947 (the founding of Eureka) and bring the guy responsible for the city back with them to 2010. Specific things have changes while others are completely the same:
Allison still had a son, Kevin, by the same father, who looks exactly the same — but is no longer autistic. This one gets lampshaded, with Henry noting that no one knows what causes it in the first place, so it would be impossible to figure out how it changed. Jack hypothesizes that Kevin may have engineered the time travel incident in order to undo his autism, but as he didn't travel back with them he has no memory of ever doing so.
Allison is no longer head of GD (Fargo is) — yet she still lives and works in Eureka (as chief medical officer).
Henry is married to a woman he previously barely knew — yet still has the same garage and equipment and is still mayor of Eureka.
GD is much more of a DoD puppet with Fargo in charge — yet all the same scientists work on all the same projects as before.
Jo is no longer deputy is now chief of GD security with her replacement being Andy the robot. And due to him never having gone through , Zane never dated her.
Tess never left for Australia so assumed that her relationship with Carter was perfect and was even moving in with him.
All of the highly improbable events that occurred in previous seasons are assumed to still have happened, like Nathan being vaporized by a rogue experiment on his wedding day.
Henry uses the term "ripple effect" to explain why little if any history has changed on a global scale: the time travel hit Eureka profoundly like a wave, causing major changes which would have caused other changes - ripples - which would have caused other changes and so on, and affected areas besides Eureka, but the further away from Eureka, the less significant the changes would be, and the ripples would eventually stop.
At the end of Angel season 4, Angel makes a Deal with the Devil to ensure that instead of being his son, Connor was raised by a normal human family. Except that Connor was an essential element to a Story Arc that lasted three seasons, involving Darla, Sahjahn, Holtz, Wesley, Lilah, and ultimately Jasmine, and the idea that his absence didn't affect any of this is absurd.
It is not entirely clear to what extent Angel's deal actually changed the past, or if it simply changed their memories. The demon who did it refers to it as shaping reality, but Angel does retain his original memories, and Connor his original genetics (or at least appearance) so if he did alter reality, the alteration was incomplete. Later in the season when Wesley undoes the spell for those within close proximity to himself, which included Connor, it is implied that they end up with memories from both timelines.
It would be very interesting to know exactly how the alternate timeline explained Wesley's estrangement from the group (implied in that his relationship with Lilah still happened) without involving Connor.
It's made very clear that the past was not changed at all, only people's memories. In season 5 they get them back.
While the exact point of divergence of the two universes from Fringe is not yet known, it's hard to imagine it could be later than about 1900 and revelations from Season 3 suggest it could possibly predate the dinosaurs. Despite this the majority of characters exist on both sides.
Barack Obama is president of the United States during the 2009-2013 term in both universes. In one of them, no one has heard of Andrew Jackson, who (in our universe) basically founded the U.S. Democratic Party that Obama belongs to.
Although it's possible this isn't an actual change, it's simply a 'historical focus' change. Andrew Jackson was fairly pro-slavery, and removed Native American, and it seems the civil right's movement in the alternate universe was different. (Eldridge Cleaver, founder of the Black Panthers here, and MLK apparently gave a 'We have a dream' speech together, and MLK is on the twenty dollar bill instead of Andrew Jackson.) So it's possible Andrew Jackson has been 'demoted' in the history books from 'important president everyone knows' to a president no one's really heard of like John Tyler, because the alternate universe has decided to skim over that part of history.
Oh, the characters don't just exist; we learn that the Bishops in both universe live in the same house and Peter sleeps in the same bedroom.
Examined in the season 4 episode "Everything In Its Right Place", where two versions of Lincoln Lee compare their lives to find out where they diverged into Captain Lee being a hyper-confident badass and Agent Lee being a cautious By-the-Book Cop, and find that their lives were identical, down to every last detail, through high school. The confident version rejects the idea that his personality has to be dictated by his past circumstances, and proposes that he's the way he is because it's what he chose to become.
In Season 6 of Supernatural an angel goes back in time and saves the Titanic from sinking. This resulted in thousands more people being alive today and many changes. However, the brothers are so central to the destiny of the world that new timeline arranges itself around them. They themselves are pretty much unchanged but the people near them have their lives altered in some ways big and small. Most likely this protection only applies to people closely connected to the brothers.
The timeline appears to be trying to repair itself in that episode however, since the plot is kicked off when descendants of the people who should have died on the Titanic start dropping off like flies. This is the work of the angry Fate, who knows Castiel organized it all to get more souls for his side of an angelic civil war.]
Played with in the episode "The One That Could Have Been" from Friends. It takes a look at the lives of the main six characters had each one had one significant change in their life: Ross never got divorced, Monica never lost weight, Chandler quit his job, Rachel got married, Phoebe became a stockbroker. In the end, by the time it's over most of their lives resemble their ones from the "real" world: Ross realizes is marriage is over while Carol gets together with Susan, Monica and Chandler have fallen in love and got together, Rachel's left her husband, Phoebe's lost her job as a stockbroker and is now performing her usual bizarre songs at Central Perk, etc. The directors commentary lampshades this:
Kevin Bright: "It would have been different, but ultimately it would have been the same."
Joey's case is an inversion, as his main "what if?" scenario is he was never fired from "Days of Our Lives" back during the events of the second season, and he's still happily employed as one of the regular cast members by the end of the episode. In the following season after "The One That Could Have Been" after learning some humility he's able to successfully appeal to the creator of the soap and is brought back. Notably, one episode that features a very brief clip from a "Days of Our Lives" episode is actually reused from the one shown in "The One That Could Have Been."
On Continuum, the time-space continuum is described as being extremely self-correcting and that most of the time even a Grandfather Paradox will not affect the major events of the timeline. In addition, a group of fanatical Time Police make sure that time travelers are stopped before they can do any real damage and that any significant changes are corrected. All of this ends up being subverted when a major historical figure travels back in time a week to change a major event in his own life and then sticks around to interact with the other time travelers already present in that time period. This is too much of a paradox and a Time Crash occurs where the entire future timeline is wiped out and a brand new timeline is created to account for all the changes.
In the Warehouse 13 episode "Endless Terror" Paracelsus goes back in time 500 years and kills the Regents of Warehouse 8. In the present, history alters so that he's run the Warehouse singlehandedly ever since, and it's now a high-tech monolith to artifact analysis and exploitation. Valdus, who in the original timeline was a Regent who made a Heroic Sacrifice, is now Paracelsus's heavy; Vanessa and Hugo reluctantly work in his human experimentation unit; and Abigail is the Wetware CPU of the Warehouse computer systems. Lampshaded by Claudia, who says the same people are drawn towards the Warehouse in any reality, prompting Pete to sarcastically wonder if MacPherson and Sykes run the break room. Artie also notes that the logos of past Warehouses show that they were associated with the same empires, indicating that Paracelsus doesn't seem to have altered history beyond the Warehouse itself.
Chrononauts has a card called "Your Parents Never Met" which forces a player to pick a new "character" card (thus altering the win conditions for said player).
Since players and characters are separate in Chrononauts, this would be logical: the original character ceased to exist and the player takes on a new one. But the new character has the same Artifacts and Mission ...
The GURPS 4th Edition sourcebook Infinite Worlds calls parallel worlds that are very similar, despite drastic divergence, "high-inertia". Probably the best example is "The United States of Lizardia", which is very similar to Earth, but with different historical figures. Oh yeah, and instead of humans there are six foot tall lizards. This is, however, explicitly noted as a "weird parallel", and there's a Lampshade Hanging in the fact that the text description of the worldline mentions that even some scientists who've been studying the USL for years "don't really believe in it".
A multiverse of infinite possibilities would mean a world where history was identical but with lizards (or bears, or triffids) would surely be inevitable.
The infinite multiverse is tempered somewhat by the inability to see or travel to universes beyond a certain number of quantum levels away. They've also only been doing it for about forty years so there would still be lots of surprises around.
"Infinite" doesn't automatically imply "all-encompassing". Just like in math you can have infinite sets of numbers that don't actually include all numbers, it's not hard to imagine an infinite multiverse in which not every conceivable alternate universe necessarily has to exist — and that assumes that it is in fact "infinite" instead of merely "finite, just HUGE" in the first place.
A character can also have Temporal Inertia as a personal trait; it ensures that he will exist in all versions of the present, as long as it's at least marginally plausible. There's also its opposite trait, Unique; a character with that one is likely to be among the first things to disappear if history changes even slightly.
Used in the setting for the RPG Feng Shui (and the card game Shadowfist). Despite time travel being involved, any changes you make to the past are likely to result in cosmetic differences in the present, at most. That is to say, killing Hitler's ancestor in 1850 would result in little more than some other short, bombastic dictator causing trouble in Germany. Even massive changes to the timeline (which are only possible by having control over Feng Shui sites) will result in the same people being born, but filling slightly different roles, similar to a different character played by an actor with limited range.
However, by controlling enough Feng Shui sites, a faction can create a major shift in history, effectively rewriting all of history from that point. Before the game started, the world was a magical world controlled by the Four Monarchs, but then the Ascended gained control of many sites and created our current history. In addition, by changing who controlled some of the Feng Shui sites in the 1930s, the Dragons caused the future, originally dominated by the Architects of the Flesh, to be overwritten.
In Chrono Trigger, a sidequest has Lucca travel back in time to prevent her mother from being crippled. As a child, she could do nothing and dedicated her life to science to prevent future accidents. If Future!Lucca succeeds, her child self still goes on the same path, for the same reasoning.
In the Legacy of Kain series of games, they describe changing events of the past via time travel as "throwing pebbles in a river." The idea being that history is resilient at self-preservation, and attempting to change it only makes the timeline diverge temporarily, before it quickly rights itself. The catch is that there is only one person/thing capable of throwing a big enough "pebble" to actually change the course of history: a paradox. So Kain goes about turning Raziel into a walking paradox so that history can be changed.
Europa Universalis and its sequel feature historical events and rulers largely unchanged from our timeline, even in the default start. Mostly averted by the third game.
There is, however, an option to enforce this upon the game. If you switch on the "Historical Rulers" option, your nation will have the same monarch names as in real life and the same relative military, diplomatic and administrative capabilities. Of course, given that a lot of nations in an average game will exist outside of when they did historically (or nations may exist that were never formed in reality) you can easily end up stuck with the same inept King for hundreds of years. With this option switched off, rulers will be generated randomly
In Eternal Darkness, three Ancients manipulated Pious Augustus in becoming their champion, but the parallel realities created by choosing one artifact instead of the two others, differs very little between them: you still end up fighting a undead roman centurion, while his patron deity still gets his ass kicked and horribly mutilated by the opposite one you summoned earlier. Which then still proceeds to try and destroy the world and enslave humanity, while your dead grandpa still fixes it for you.
Subverted by the fact that the first aligned rune you find is dependant on wich one you choose at the beginning (on a Rock Paper Scissors system from weakest to strongest against). Since it can help replenish health (VERY useful), sanity (useful if you're very low on it) or mana (worthless as it drains the same amount it replenishes), guess why people tend to leave Xel'lotath's artifact for last...
Persona 3 Portable has a female option to see what would happen if the protagonist were a bright female girl instead. The answer? Aside from Shinji's life being extended some (he would still die shortly thanks to the suppressants), not much of anything.
Bioshock Infinite uses this to provide a meta commentary on the nature of video game storytelling and how the player interacts with it, through the theme of "Constants and Variables." There is always "a man, a lighthouse, and a city," and while there are a few points in the story where you are presented with a binary choice, it has no effect on the ending or the path you take through the story. Certain events are fixed, such as the fact that Booker never rows to the lighthouse, the coin always comes up heads, and he always picks ball #77 at the Raffle, even after being explicitly told not to. On a meta level, the plasmids and weapons at your disposal, as well as environments that support multiple approaches, mean that the number of ways a given playable encounter can pan out are effectively infinite, just as the title suggests. But the major beats of the story, especially the ending, will always happen exactly the same way no matter what.
In Steins;Gate, the main characters are successfully able to alter the circumstances of transgender Ruka's birth so that she is born as a normal female. However, literally every single other thing about her—appearance, behavior, relationship to other characters—is exactly the same. The only real change is a minor event earlier in her life that results in an artifact important to the plot being broken in the new timeline.
El Goonish Shivemultiverse. In the main story world Tedd has serious self-esteem issues. In the "alpha dimension" Tedd — but not his friends — exists and apparently has enough of self-esteem issues to flip out, become Evil Overlord and try to kill his alternates. In yet another Alternate Universe ("Second Life") aliens fought in the American Revolutionary War, Ellen's best friend and crush are both Half Human Hybrids, but... guess what? Tedd still exists. And still has self-esteem issues.
I think Dan said, at some point, that every possible dimension has a Tedd.
Besides there always being a Tedd, all female versions of him shown so far are in relationships with Elliot.
And all female versions of Elliot shown so far, sans the Second Life universe. (Though Tedd's counterpart wanted a relationship with Ellen, the closest thing to a female Elliot that universe had.)
In The Adventures of Dr. McNinja, Chuck Goodrich, The Mayor came from the future to prevent a zombie apocalypse. However, somehow, increasingly ridiculous global tragedies always end up occuring in the new future, and it's always Chuck Goodrich, AstronautChrononaut who finds a time portal in space that allows him to prevent it. It has yet to be revealed whether there's a reason for this or if it's just Rule of Funny.
There's sort of a reason for it. When you travel back in time to fix something, you don't actually prevent the Bad Thing from ever happening; you create a quantum split at the point you emerge in the past that creates two universes; one where you didn't arrive, thus creating the timeline you lived through that was so shitty you had to go back and fix it, and one where you did arrive, thus allowing you to avert the Bad Thing you came back to prevent, but in all likelihood there's going to be another Bad Thing that's just as cataclysmic rolling down the track in its place, which will send the newer, younger you traveling back through time to fix that (Chuck has apparently done this at least five times).
Future King Radical Hand Waves it with: "Time travel is a difficult art with few experts. There's a reason it's always Chuck Goodrich. He's the best."
In the post-scratch session many things that you'd expect to have changed stayed pretty much the same. For example, Jane and Jake still talk in Anachronism Stew-style old-timey speech, plus Jake still has an interest in firearms and fisticuffs.
Also, while not nearly as much is known about pre-scratch Alternia (Beforus, actually) as post-Scratch Alternia is — despite the drastic difference in troll society, some things appear to have stayed the same. The trolls still had two 6-letter names, trolls were still adopted by lusii, and it was implied that the quadrant still existed (although it probably wasn't enforced as strictly).
In DM of the Rings, the players are being railroaded through the plot of The Lord of the Rings by a Dungeon Master with an iron fist. However, Legolas's player slips the DM's notice for just a little too long, who winds up killing Gollum during the events of Fellowship of the Ring. Despite this, Frodo and Sam still make it through Mordor, though largely because their players quit so the DM turned them into NPCs so he could gloss over the events of their journey.
In Decades of Darkness, Napoleon manages to win the battle of Waterloo, only to lose against the Prussians under Blücher afterwards, making "Waterloo" in this world the synonym of "a victory claimed too early".
And most people in-universe think that the secession of New England was inevitable, going as far as stating that * Americans and Yankees are different people.
In Red vs. Blue Church gets the opportunity to save himself and his friends, but despite every butterfly he tried to stomp on, some other event kicks in and the only thing he changed is that he is the one who cause him team's eventual demises. Except Gary the liar turns out to have sucked Church the AI into a simulation where everything was his fault.
In Green Antarctica, something happened so that Antarctica didn't have the glaciers and ice sheets that they did in OTL. Yet World History still went on the same until the Tsalal got into the picture.
In Red Dawn +20, the Chernobyl disaster still happened as scheduled, but this time, instead of Soviet engineering incompetence, it was American military intel incompetence that destroyed the reactor. Intel said the reactors weren't online when they were set to be targeted. Oops.
Despite a background universe that features superheroes and villains, man landing on the moon in 1962 instead of 1969, four alien invasions, a general higher technology level, and so on, the Global Guardians PBEM Universe has pretty much followed the real world's timeline.
In addition, the setting's "multi-verse" is based on the idea of the multiple-world hypothesis, in which every time any person makes a choice, a new alternate timeline is branched off that reflects those choices. However, timelines that are based on irrelevant choices (for example, having toast and eggs for breakfast instead of cereal) tend to re-merge further down the time stream with all of its similarly irrelevant alternaties.
In the Whateley Universe, despite the fact that the world has a Lovecraft Lite mythos, ancient Sidhe, mutants with superpowers, and supernatural monsters, the world is pretty much the same as what we're used to. Apparently, all the great scientific and medical advancements thanks to super-inventors have been cancelled out by bad stuff due to supervillains and mad scientists.
On Wrestle Crap, Rewriting the Book has some stories that end up like this in some way.
In "What if Vince McMahon wasn't the Higher Power?", Jake the Snake is the Higher Power, winds up getting control of the company and Stephanie... and in the end, the Ministry is dissolved and Vince is removed from TV albeit by order of Austin, who gained control of the company from Jake in a match.
In a recent story about what would happen if Goldberg's streak hadn't been broken, regardless of everything that changes as a result of this, WCW still collapses. Word of God says that this was the whole point of the story (that WCW's eventual, inevitable collapse wasn't due to one particular incident, but that they would have found some way to screw up and fail no matter what).
If DX had gotten into the Norfolk Scope Arena that fateful night, WCW would still have collapsed, apparently (but they would have gotten bought instead by ECW, which wound up becoming successful and eventually becoming Ring of Honor in all but name).
Fandom circles on websites like Tumblr or Livejournal tend invoke this deliberately with the joke "AU in which everything's the same except _____".
The Simpsons episode "Treehouse of Horror V" segment "Time and Punishment", which begins as a parody of "A Sound of Thunder" and gets progressively weirder — but no matter what changes Homer makes to history, there's still a Simpsons family, and they're still living in the same house. (Granted, the house is in various permutations of history a McDonalds, a Sphinx with Bart's face, and a giant shoe a la the Nursery Rhyme, but the Simpsons live there nonetheless.) The story ends with everything normal, except for people having long, forked, prehensile tongues. "Eh, close enough."
For that matter, some of the opening credits' "sofa gags" might constitute close parallel universes of their own.
On Danny Phantom, in "Masters of All Time", Danny goes back in time to prevent the accident that gave Vlad ecto-acne and his powers... and he succeeds in this, but Jack gets hit with the blast instead, becoming half-ghost in Vlad's place. Apparently somebody had to fill that role. Not only that, but Jack's ghost form has the exact same costume that Vlad's has in the real timeline... with no real explanation as to why this should be.
Family Guy has the Road to the Multiverse episode where Brian and Stewie travel through different alternate realities including one where the Japanese won World War II, another where people have two heads and another one where dogs are the dominant sentient species and keep humans as pets. In all of them Quahog and the main characters exist, with the only apparent exception being a world where the last Ice Age didn't end and the town's place is occupied by a glacier. The first world they visit is even stated as one where Christianity never existed, and yet St. Peter's Basilica still exists and is identical to ours... except the Sistine Chapel consists entirely of Jodie Foster's portraits painted by John Hinckley Jr.
In a more heartwarming example, there is the episode "Forget-Me-Not," in which Peter, Brian, Joe, and Quagmire wake up after a car crash, with no memory of themselves or each other. This trope comes into play when it is revealed that the entire situation was fabricated by Stewie, who wanted to challenge Brian's claim that he and Peter would be friends regardless of how they met. Turns out Brian was right, as the two end up defending each other in the end of the scenario. Stewie even admits that the two are destined to be friends. D'aww.
Also, the sensation of a cutaway exists despite the fact that none of them have memories to cutaway to.
In Futurama, the crew is sent back in time to Roswell, creating the famous UFO crash landing (it's Bender's mangled body). Though an effort is made to not alter history, Hilarity Ensues and Fry ends up becoming his own grandfather. At this point, the Professor is just fed up and mounts a full-blown assault on Roswell Army Air Field with the Planet Express ship, stealing a radar dish so they can return home. History is not affected in the slightest.
Professor: Choke on that, causality!
On the other hand, if the alternate universes presented by the What-If Machine in the "Anthology of Interest" stories are accepted as true, then Fry becoming his own grandfather is a set point in time that can't be avoided (in the AU where he never goes into the future, his destroying the Cryo-Chamber destroys the universe). In other words, the events of the Roswell episode are quite possible all part of a Stable Time Loop - the assault and its aftermath might well be events unrecorded by history (especially given its unreliability back in the 1940s-50s, including the lack of advanced technology to record such events as faithfully as in the present). But who can say for certain?
World War One, despite being set off by a VERY unlikely catalyst, was just a powder keg waiting to blow. Not guaranteed, but still highly likely.
Speaking of that trope, killing Hitler likely wouldn't have done much to keep the Nazis from taking over Germany or the Holocaust from happening, either, assuming of course that World War One still happened. The Nazi Party already existed before Hitler joined it (in fact, he was originally employed by the government to spy on them), and Hitler, while a charismatic figure who was good at riling up the populace with his fiery speeches, was not much of a strategist and most of his successful ideas came from other, smarter guys in the Nazi top brass. So basically, if it hadn't been him as the head of the Nazi Party, it could have easily been someone else who was similarly charismatic and good at making speeches. (But since the numerous factors you'd have to manipulate to prevent the Nazis from rising to power would make for a much more complicated, less exciting plot that just trying to assassinate one guy, this is an arguably justified case of Hollywood History.)
And if not the Nazis, a militaristic dictatorship of some sort was still likely, given that in the 1920s/1930s such governments were appearing all over the world from Japan to Europe to South America.
Since we are on THAT subject, even if the Nazis had never come to power, Japan would still be a militaristic, expansionist empire. Considering the fact that the catalyst of America's entry into the Second World War was largely due to actions taken by Japan note America put an oil embargo on Japan for invading China and imposing a brutal regime on what had been an ally of the U.S, if an unreliable one. The oil embargo made the Japanese leaders seriously consider attacking America, thus leading to Pearl Harbor. America might not have even entered the war against Germany had Hitler not declared war on the U.S, thus launching a fight against three huge world powers. , so in all likihood, even if by some miracle the economic destabilization of Germany didn't cause some nutcase to rise to power and cause a war in Europe, there is a good chance a major war in the Pacific between America (with Britain and the Netherlands potentially along for the ride) and Japan would have still happened.
It is generally agreed among serious historians that despite the legions of "What if?" alternate historical fictions out there, neither the American Confederacy nor Nazi Germany had a chance. If things had gone differently, the conflicts may have been longer or shorter or more or fewer people may have died, but given the general circumstances, you don't win wars without a Navy or invade the USSR while your other enemy develops nuclear weapons, even if you had a tank powered by steampunk or a magnetic powered UFO-bomber. Its never been a matter of debate of whether the US would be celebrating Jefferson Davis' birthday if things had gone differently, is merely a question of whether 700,000 Americans would have died vs. 500,000. Likewise, if things had gone better for Nazi Germany, the only difference would be that parts of Berlin would still be slightly radioactive.
Assuming, as pointed out above, that the US would have entered the European theater without Germany declaring war on them. The moment the first assumption is made, the degree of uncertainty grows. The problem is that you can't know which nails are proverbially spiteful, and which ones are not.
The Science of Discworld books argue that this applies to most things, although it focuses particularly on science and technology. Advances never come from a lone genius working in a vacuum, they happen when advances in knowledge and technology combine with an actual use for some new advance. For example, steam power had been known as a curiosity for thousands of years, but the invention of a useful steam engine and the industrial revolution occurred once technology had advanced enough to allow a practical engine to be built and society actually had a need for such an engine (initially as a pump for deeper mines, which hadn't been necessary or possible in the past). Similarly, while Darwin is often held up as the father of evolution, he was merely the first to really codify ideas that many others, including his own grandfather, were investigating. If someone went back in time and killed Darwin, our knowledge of evolution wouldn't disappear, we'd simply talk about Wallace's theory of evolution instead.
Much has been made of the rise of The Beatles in the US happening in the aftermath of the JFK assassination, implying that Americans embraced them as a way to cope with the blow their collective psyche had taken. In fact, Capitol Records had been planning a huge promotional push for The Beatles starting in January 1964. Ed Sullivan actually booked their February 9th appearance in November, based in part on the craze they'd set off in Britain.note though some people have tried to argue that British Beatlemania was also an attempt to cope with a blow to a national psyche, from the Profumo scandal Odds are that even if Kennedy had left Dallas unscathed, American Beatlemania would have spread exactly the same way it did. One notable variable that might actually have altered things a bit was when some DJs obtained copies of the Parlophone 45 of "I Want To Hold Your Hand" and started playing it in mid-December, forcing Capitol to release it right after Christmas, a month ahead of schedule.
Another Beatle-related one: Bob Dylan allegedly introducing them to marijuana in 1964 and thereby setting much of The Sixties in motion. For one thing, several of them had already tried cannabis (and other drugs) during the Hamburg years, so it was more of a re-introduction. And with drugs gaining popularity in the emerging Swinging London scene at the time, The Beatles would have been introduced to them sooner or later anyway.