"...we now live in a world where kings and noblemen rule the roost. And they've turned all of central Europe — our home, now, ours and our childrens' to come — into a raging inferno. We are surrounded by a Ring of Fire. Well, I've fought forest fires before. So have lots of other men in this room. The best way to fight a fire is to start a counterfire. So my position is simple. I say we start the American Revolution — a hundred and fifty years ahead of schedule!"
The problem with the past is that it's so uncivilized, but any time traveler worth their salt can fix that. Just introduce it to the delights of modern technology, several centuries early. You may need to go through a few intermediate stages, replicating the history of technology on fast forward, but you know exactly what needs doing. How difficult can it be?
There are two types of time travelers who try this stunt - the unwilling ones, Trapped in the Past with just the right skills needed to jump start the industrial revolution, and the reckless ones who don't care about paradoxes, they just want to rewrite history for the better.
Either way, this is a long term plan. Even optimistic heroes will expect to take a few years to get the desired results. Realistic ones will consider it a lifetime's work. The hero can't leap straight to modern technology; they have to get the past society to go through all the intermediate steps first, or they won't have the necessary tools to make the tools to do the job. As such, this is typically the plot of an entire book, or even a series.
Ancient Astronauts and explorers rediscovering lost colonies occasionally fall into the trope, if the story goes into detail about how they introduce technological advances, but they normally gloss that over. By contrast, works in this subgenre typically go into great details about the new technologies being introduced to the past, and their social impact, as well as addressing all the problems that would realistically crop up.
If the stranded party has a phone to a high-tech society, whether in the future or on another world, this trope can still apply. The phone can provide them with all the information they need, but they still have to deal with the immense practical problems involved in getting from medieval to modern technology. It would still take decades to get 14th century England from church bells to digital clocks, even with an internet connection to the present day, and the full resources of the kingdom at your disposal. However, if the stranded party can get actual physical objects from their high-tech friends, the difficulties melt away, and this trope does not apply.
If a Hero succeeds, there's still a risk of going horribly wrong, going horribly right, or both.
Fridge Logic would dictate that this would result in an infinite technological loop: Suppose the radio was invented back in 50 B.C. by a time traveler. Since this means that time travel is possible, eventually somebody from the future of the timeline created by the original time traveler would travel back to an even earlier time (for example, 800 B.C.) and give radio to the Akkadians or something. Then a time traveler from that timeline would introduce radio even father back, repeating until the very first generation of humans ever to evolve is given advanced technology and civilization.
Basically the background of the Zaibach Empire in The Vision of Escaflowne: Emperor Dornkirk (who was in this reality Isaac Newton) brought the gift of science, culture and technology to the weak, incompetent farmer-nomads of the Zaibach area in Planet Gaea, developing themselves into a force able to defend themselves, eventually build their own industrial civilization, and eventually turn into a warmongering empire.
In Maoyuu Maou Yuusha, the Demon Queen, a peace-seeking sort despite her name, consorts (literally) with the opposing Hero to bring modernizations to farming, industry and navigation that help humanity avoid the need for war. Expected pitfalls are expected by the Genre Savvy leader as not everyone on either side of the war is willing to cede control over those who once lacked control of their destinies or did things that others expected because of their heritages.
The Marvel 1602 mini-series has a time-displaced Captain America sent back to Elizabethan times. When asked to return to the future, he insists on staying to try and build a better America from the beginning — which he does in small ways, such as helping a group of colonists survive a winter that should have wiped them out, or warning the natives against selling their land to unscrupulous capitalists. The final touch comes when, because of his actions, the American colonies declare independence from Britain 174 years early.
It also has consequences beyond his control — his presence causes the Marvel Universe to impose itself on the past, and period versions of the X-Men, Avengers and other superheroes start appearing.
This is the premise of Jonathan Hickman's Pax Romana. The ailing Catholic Church sends a paramilitary group back to 312 AD to use both advanced technology and knowledge of future events to help the Roman Empire set up a stronger foundation for the Church. Things don't go as planned, but even so, technology and culture advance much quicker than in the unaltered timeline, giving rise to a utopian society.
The Argentine comic El Eternauta (second part): the protagonist decides to give to a tribal After the End civilization of the future, enslaved by an alien race, knowledge of modern weaponry and machinery. Since the available tools and labour skills are quite crude, they can't go beyond mid-XIX century tech: simple pistols, muskets and cannons and basic steam engines (making it a Steam Punk comic in 1976).
One What If? story (in v1 #33) featured Tony (Iron Man) Stark becoming trapped in the time of King Arthur. He starts advancing the technology level singlehanded till he can recreate his Iron Man armor.
In a Tim Traveller story, Tim is annoyed that his dad doesn't get modern technology, so decides to remedy it and goes back in time to show his laptop to some cavemen. They don't understand it and just try bashing it, which leads them to invent fire.
In the Comic Book Adaptation of Its About Time the astronauts build a giant mousetrap to trap a giant rodent. How they managed t smelt the metal used in the thing isn't brought up.
Saruman Of The Many Devices The basic premise is this - the titular character aided by a rather benevolent AI introduce renaissance-era technology, including fairly advanced steelworking and of course guns to Middle Earth in an attempt to bring forth an industrial era. Specifically, to the Uruk-hai working for him already.
Crusade In Jeans had The Hero do this too, by using the assembly line principle along with an Ipod to bribe the baker to bake a lot of bread overnight.
The Philadelphia Experiment II combines this with Set Right What Once Went Wrong: A stealth aircraft armed with nuclear bombs is accidentally transported back in time to Germany in 1943, where it's captured by the Nazis and used to bomb several cities in the eastern United States (including Washington, DC), with the end result that the Axis Powers won World War II. Needless to say, the protagonist from the original movie is the one who winds up having to fix this mess.
This is combined with Low Culture, High Tech when the aircraft is destroyed on its final run. The Nazis, of course, want another and the scientist who claimed to have invented it can't replicate one. In the revised history, his son trying to clear the family name.
Sengoku jieitai 1549 (also known as Samurai Commando: Mission 1549) features failed experiment which leads to time travel of a wounded samurai to our times and a group of soldiers to the year 1549. When the second group of soldiers goes to 1549 in a search and rescue mission they discover, among other things, a refinery.
Minor example in Night at the Museum. Larry accidentally left behind his smartphone back in post-WWII United States (specifically, VJ Day), and a passing seaman picks it up, takes it home, and takes it apart. The seaman's name? Joey Motorola.
Played for Laughs in Hot Tub Time Machine - one of the characters decides to stay in the 1980s instead of returning to his present, and spends the intervening time becoming a billionaire by getting in on the ground floor of every important innovation since between then and now.
Poul Andersonshowed the problems with this in his short story The Man Who Came Early, in which an American soldier stationed in Iceland is sent back to the Viking Era after being hit by lightning. Luckily the Icelandic language has not changed much since then. All his attempts to change history fall flat on their face. When he tries to show the Vikings how to make compasses, he has no idea where to find or mine magnetic ores. When he tries to show them how to build more modern sailing vessels, the Vikings point out that such vessels are too cumbersome to dock anywhere where there is not a ready built harbor, an obvious rarity in that time period, and so on. The story's main point is that introducing future inventions is immensely difficult because most advances are useless without an advanced societal infrastructure to support them.
Also his contribution to Harlan Ellison's Dangerous Visions, "Eutopia", is about an alternate world where Alexander the Great solidified his Empire and the Greeks are still ruling the world in 1960 AD (or thereabouts).
Happens IN SPACE! in the Larry Niven novel Destroyer Of Worlds. A lone Pak (a highly intelligent, super strong, long lived creature) gets stranded on a primitive world. He introduces the natives (who have Bronze Age technology) to technology in steps, hibernating for unknown periods between each step. He needs to do this to escape the primitive world, by reaching the ramscoop level.
The Cross Time Engineer and sequels by Leo Frankowski. Polish hiker Conrad Schwartz, in a drunken stupor, bypasses all kinds of security and stumbles into a historical-research time portal (created, coincidentally, by his cousin) and awakens in thirteenth-century Poland, where he has just ten years to industrialize and unite his nation before the Mongol hordes arrive and kill everybody.
This one has been accused of being one big bit of Mary Sue-starring wish-fulfillment. Bad enough the original publisher dropped him so the later novels are self published.
Language difficulties are hand waved in a justification that "all Slavic languages are pretty much the same." Diseases don't really rear their head until the 6th and self published book, Conrad's Quest for Rubber where they have to deal with unfamiliar diseases in Africa, but is semi-justified by Conrad's cousin going back in time to make Conrad sterile (no, not like that... he's rather prolific, really).
It does not help that the author 'cheats' by having the time traveling cousin provide Conrad with all sorts of help that makes Conrad way more effective than he should have been and saves his life when Conrad's actions are about to get him killed.
An alternate timeline is mentioned where one decision by Conrad from the first book changed the outcome of everything. The alternate Conrad failed to get the patronage of a powerful lord and was not able to accomplish anything on his own.
In Terry Pratchett's short story Once and Future a time traveler called Mervin finds himself not only trapped in the past, but in a past that never existed; the Anachronism Stew that was King Arthur's time. Working as a doctor for a village in Sir Ector's demenses, he quickly realises that what they need is a great and noble leader, gimmicks up an electromagnet to hold a sword in a stone, and waits for a candidate whose body language suggests he's sensible enough to take advice. It works, although not quite how he expected.
Nimue Alban's situation in David Weber's Safehold series lacks time travel, but otherwise fits perfectly. Nimue (or rather a Ridiculously Human Robot with her personality) is awoken in the last human world of Safehold, which has been trapped in Medieval Stasis for almost a millennium thanks to its delusional founders. Nimue's objective is to undo this and bring humanity back into the era of space travel. Many details listed in the description are averted, since robots can't get sick, and Nimue has to learn Safeholdian English before she can venture out among its people.
For those who don't get the joke, she switches from the name Nimue Alban (Nimue as the lady in the lake, and Alban as in England) to Merlin.
Alban is the Gaelic form of Scotland, England is Albion (and it's in French)...
Merlin/Nimue is aided in this task since this was planned out rather thoroughly and included a library computer, some advanced equipment and a limited manufacturing capacity. Of course there was also the unexpected bonus of Baron Seamount and Edwyrd Howsmyn.
Lest Darkness Fall by L. Sprague de Camp. Martin Padway is struck by lightning and finds himself in sixth-century Rome, on the verge of its ruin at Justinian's hands and the onset of the Dark Ages. He may be able to save civilization, if he can only get the ruling Goths to grasp the value of his innovations. Notable as it does take a few tries to figure out what does and does not work...
Also notable in that one of the first and most important inventions he introduces is brandy. In itself, useless. For making money and building a place in society, invaluable.
Brought later full circle with To Bring The Light by David Drake, which is bound with Lest Darkness Fall in some editions. In this story a woman from Justinian Era Rome gets sent back to the founding of Rome and must use the inventions of later Rome to help found it...
As a Take That to Lest Darkness Fall, Frederik Pohl wrote the short short story "The Deadly Mission of Phineas Snodgrass." Snodgrass gives the Romans modern medicine and agriculture…but not birth control. Oops. The exceedingly overpopulated alternate timeline he created decides to do something about it. For added fun, it explicitly mentions the de Camp story.
Temporally inverted in Philip Francis Nowlan's Armageddon 2419 A.D., or as it's better known, Buck Rogers in the 25th Century. Rogers, in the various versions of his tale, brings lost knowledge and a certain 20th-century vitality to future America and/or Earth as a whole.
Lord Kalvan of Otherwhen by H. Beam Piper. Pennsylvania cop Calvin Morrison runs afoul of the Paratime Police and is accidentally transported to a medieval alternate Earth where a corrupt theocracy controls the secret of gunpowder. Pretty realistically handled — he knows the basic formula, but also knows that there were steps in making it consistent that he needs to rediscover, and he has to convince wary leaders to build up the entire infrastructure for gun manufacturing from scratch.
Harry Harrison's Deathworld 2 features a non-time travel version of this, in which interstellar adventurer Jason dinAlt is stranded on a Lost Colony which has regressed to barbarism. Various bits and pieces of more advanced technology, generally regarded more or less as sorcery, are held as closely guarded secrets by the different clans (one group still knows how to make primitive petroleum-fueled engines, another how to make some crude electrical devices, yet another clan practices alchemy-level chemistry). The hero winds up completely revolutionizing the planet's backwater society solely out a desire to get off that primitive dirtball and back to someplace more civilized. The language issue is avoided as everyone on the planet speaks a (somewhat degraded) version of Esperanto.
In one of Harry Harrison's The Stainless Steel Rat novels, the main character ends up in a pocket universe that contains an alternate version of the Napoleonic Wars, in which the Big Bad gives Napoleon 20th century artillery. Napoleon, already an artillery genius, uses the technology to easily beat all of Europe into submission. The main character has to explain to an English nobleman the mechanics of one such cannon, who then uses it to sink a ship with a few shots.
Interestingly, Jason manages to make working engines despite claiming that no one knows how internal combustion engines work anymore.
The Other Time (started by Mack Reynolds, completed by Dean Ing after Reynolds' death) features a modern day (1980's) anthropologist doing field work in Mexico who gets thrown back in history to just the right time to run into Cortez and the conquistadors. The language issue is avoided as the hero (being an anthropologist) naturally speaks Nahuatl and Spanish.
The computer engineer among the "Rivington men" of The Guns Of The South, who says that if and when the computers they brought back to Confederate America break down, he won't be able to fix them, because the time period doesn't have "the tools to make the tools to fix them, and probably a few iterations after that." Reproducing AK-47s though, is within their grasp (see Afghani copies of the AK-47 made in the 1980s).
Also something of a deconstruction, with the Rivington men outright telling the Confederates (at least prominent ones like Robert E. Lee and Jefferson Davis) that they're time-travelers, and then the Southerners successfully defeating them despite their technological superiority when they turn against them.
Belisarius Series: Two factions from the far future, one attempting to make a future hostile to transhumans, the other trying to save a tolerant future. Neither the future that was, nor the future if The Bad Guys Win happen, as a new Golden Ending happens significantly different than ours.
And he later tries to modernize the Lamuellans. The only invention he succeeds in introducing is the sandwich. They take it very seriously, though, and Arthur's position of divine sandwichmaker gets him even more respect than the village chieftain.
A bit of a Deconstruction: Arthur doesn't know how to make anything but sandwiches. Because Arthur is the consummate average man, he doesn't understand most of the technology he's familiar with. If you were in Roman times, could you make a digital camera? Thought not.
John Barnes's Timeline Wars trilogy: Patton's Spaceship, Washington's Dirigible, and 'Caesar's Bicycle all see this trope used, as part of a multi-universal time war against Carthagian descended timelines.
Isaac Asimov's short story The Red Queen's Race is about a man who attempts to do this to ancient Greece, sending back modern knowledge with the intention of getting the scientific revolution going in classical times and giving the world a two-millennium head start. However, the professor who did the translation into ancient Greek realizes what was up, and so deliberately included only such information as would explain certain before-their-time theories that really did appear in ancient times, thereby creating a Stable Time Loop.
A variation from K.A. Applegate's Everworld series: the heroes, while trapped in a Fantasy Kitchen Sink alternate world, introduce telegraphs to an Elven city, and use the technology to get rich.
Conversed in Kir Bulychev's short story "Паровоз для царя" (lit. Steam locomotive for the tzar), where the characters discuss how hard would it be to pull this off in Real Life: if you were to give the tzar the technology of automobiles, you'd first have to explain to him the workings of petrochemistry (assuming he'll listen to your ramblings at all). Oh, and you'd better be an expert in petrochemistry and engineering in general.
In Vernor Vinge's A Fire Upon the Deep, two groups on a medieval planet get technological advice, but not physical help, from stranded human children with, respectively, a small computer and an FTL phone, allowing them both to advance significantly. It helps enormously that the child's computer has a full history of technology stored, while the people on the other end of the phone can look up theoretical academic research on bringing technology to lost colonies, which is apparently a minor academic discipline in that galaxy.
Referenced/averted in 'The Golden Crown'- Maegen decides that radios would be useless, and brings mini chocolate bars and ball-point pens to trade to the Romans instead.
A very short story Ask Caesar by Yevgeny Lukin and Lubov Lukina is an attorney's speech in court. His client is accused of attempting to change history by teaching modern science (up to quantum physics) to Cro-Magnons. "But did it change anything? No." Except for some insignificant details, like the fact that Gaius Julius Caesar has been diced with lasers.
In Just War, an incautious time traveller accidentally gives the Nazis a technological leg-up, resulting in them developing stealth bombers in time for World War II.
In The Room With No Doors Joel explains to a 17th century Japanese warlord how to turn a loom into a calculating engine. He's surprised at how quickly the warlord catches on, and comes up with uses for computers that Joel thought he'd have to lead up to.
A fantasy version is introduced in Guardians of the Flame where Lou Riccetti's wizard character renounces his magic only to start using his engineering knowledge to overturn Medieval Stasis in their fight against slavery. Predictably, the opposing factions, although not privy to the details of things such as how to make gunpowder, find ways to adapt the technology through magic.
Time Scout: Sort of. One downtimer gets his hands on uptimer materials and eventually discovers his way through the gates to La La Land.
In the Doctor Who New Adventures novel Just War, an incautious time traveller accidentally gives the Nazis a technological leg-up, resulting in them developing stealth bombers in time for World War II.
The first book of Alex Scarrow's Time Riders Series has a man intentionally travel back to 1941 a) to give Hitler a ton of future tech, b) to convince Hitler not to invade Russia and c) to take over Nazi Germany himself. In the end, German steamrolled most of Europe and a good deal of the USA in twelve years, with Russia and China next on the schedule. Hovercrafts and pulse rifles tend to give you an advantage. Did I forget to mention the guy did this intentionally?
A group or community is transplanted.
The Islander Trilogy by S.M. Stirling. The island of Nantucket is whisked into 1250 BC, and must contend with Bronze Age cultures and their own crop of power-hungry renegades. This one does contend with language difficulties, uptime diseases, and so forth; the Nantucketers manage to wipe out huge numbers of Native Americans before they even realize what's going on, because the first party sent to the mainland contains someone with a sniffle. Their language difficulties are moderately eased by the fact that the languages of Europe are, at that point, much closer to still being "Proto-Indo-European"...
Also helped by Nantucket being big and upscale enough that having a professor of ancient languages on it at the time isn't ridiculously improbable.
The Assiti Shards milieu by Eric Flint and others. Cast-off shards of transdimensional alien "art" bombard Earth and transpose large chunks of it with other times and places. Several alternate histories are planned in this meta-setting, including Time Spike (several separate Shard events deposit a modern maximum security prison, the Cherokees on the Trail of Tears, a band of conquistadors, and multiple pre-Columbian Indian settlements into the Cretaceous), 1776 (the armies of George Washington and Frederick the Great both find themselves in ancient Rome during the Crisis of the Third Century), and By Any Other Name (the Assiti themselves make unwilling contact with Elizabethan England), but only two have seen any publishing. The first one has, however, seen a lot:
1632 and many, many sequels. The West Virginia coal-mining town of Grantville is translocated to southern Germany in the middle of the Thirty Years' War, utterly shattering the power structure and world view of Reformation Europe. Once again, this setting deals with language and diseases fairly well. Although in this case, it's the uptime people of Grantville who have to worry about the risk that the pandemic plagues of the 1600s will devastate their community. On the bright side, they're at a recent enough point in the past that their English is recognizable in England, and their German-speakers are understandable to the Germans around them.
In many ways, the real shockwave comes from the introduction of modern political ideas such as egalitarianism and religious tolerance. One major player in the setting is the Committees of Correspondence, an international organization made up almost entirely of downtimers devoted to promoting democracy, freedom, and sanitation across Europe. They look something like a cross between the Sicilian Mafia and the Sons of Liberty.
The Axis of Time trilogy by John Birmingham. World War 2.1: Weapons of Choice, World War 2.2: Designated Targets, and World War 2.3: Final Impact. A multinational naval task force from 2021 is sent back to World War II, where it (literally) impacts with the American fleet steaming for Midway. The consequences are extremely far-reaching.
And there's even a nod to The Guns Of The South in that while the up-time multinationals can easily reproduce the AK-47 and "low-tech" (for the early 21st Century) gear, their more advanced devices can't be duplicated because the composites, chemicals, or specific materials can't be manufactured with 1940s-era equipment.
Not just the uptimers. The Soviets manage to do the same by studying the databanks aboard the Vanguard. The Nazis and the Japanese also make some small advances, but not many.
Also, the American and British versions of the AK-47 feature underslung grenade launchers, making them much more effective in combat. By the third novel, all the uptimer ships and troops are forced to "downgrade", as their ammunition has run out. This "downgrade" is still superior to what was available in the 1940s, though. They've been able to reproduce the fuel mix used by ships, though.
A somewhat similar story can be seen in the manga and anime Zipang. A good chunk of the plot is about whether or not to give the metaphorical radio to the metaphorical Romans.
The Destroyermen teach their initially Bronze Age Lemurian allies how to build and use pretty much anything they can dream up. They have a good reason for this: the series' Big Bad is a race of dinosaur descendants that think humans and Lemurians are crunchy and good with ketchup. So far the technologies transferred include (in roughly chronological order): modified Greco-Roman infantry tactics and weapons, gunpowder and cannons, oil drilling, the Bessemer process, steam propulsion, muskets, electricity, seaplanes, and of course, radio.
On the other side, the transplanted Japanese end up in the hands of the Grik, and are forced (in some cases, no forcing was necessary) to teach them new things. Several books later, the Grik start building seagoing ironclads, blimps dropping kamikaze bombs, muskets of their own (albeit cruder because of the Griks' claws), and artillery (including anti-air variants).
In the first book in the Honor Harrington series, the Havenites introduce Civil War-type firearms to some of the natives of the planet Medusa, who are at a Bronze Age level of technology. Their plan is to have hordes of Medusans armed with primitive firearms, not to mention hopped up on a combination of religious fanaticism and the local equivalent of PCP, massacre the human enclaves, and convince the Manticorans to abandon the planet completely, giving Haven the opportunity to move in. They get found out, and the Medusans run right into a force of Royal Manticoran Marines, but the Manticorans note bitterly that they now have no choice but to introduce the weapons to the more friendly Medusans, so the Medusans can defend themselves. The long-term consequences of this are not shown, as the series never revisits Medusa.
A variant occurs in the second book, where the Manticorans introduce advanced technology to the (relatively primitive) planet Grayson, while the Havenites do the same with Grayson's fratricidal sister planet, Masada. Here, the tech gap is much narrower, as the Graysons and Masadans are well ahead of modern Earth, just way behind the Manticorans and Havenites. In the climactic battle, the Masadans have hijacked a Havenite warship that would normally make mincemeat out of the Manticoran ships, but the Masadans don't know how to properly operate it. In later books, the Graysons catch up with the Manticorans, to the point that the Grayson Space Navy is probably the fourth best in the galaxy (and the Andermani and Havenites only win by sheer numbers).
A non-time-travel example in The Lost Regiment. After the Battle of Gettysburg, the 35th Maine boards a ship along with an artillery batallion, and the ship is tranported by a Negative Space Wedgie to another planet (the two moons are a dead giveaway). There, they find numerous city-states founded by humans who have been transported there throughout history. This includes ancient Russians (the first culture they meet), Carthaginians, Romans, Mayans, and others. They also find out that the rulers of this world are 10-foot-tall Human Aliens divided into several hordes that are engaged in never-ending circles around the planet at different latitudes, demanding and receiving tribute from the human city-states in the form of crops, materials, and people for food (their word for humans is "cattle"). It's not long before one such horde, the Tugars arrives to collect their generational tribute and put the newly-arrived "Yankees" in their place. After helping the Russian peasants rise up against the boyars and the chuch, the Americans resolve to turn the city of Suzdal into a modern (i.e. Civil War-era) industrial power with a modern army with firearms. Unfortunately, they only have a year before the main body of the horde arrives. Many of the soldiers are former factory and mine workers, so they are familiar with the methods of industrialization. However, making Civil War-era rifled weapons requires precision tools, so they, instead settle for Revolution-era muskets and smoothbore cannons. They even build an observation balloon and a working locomotive. By later books, they move on to seagoing ironclads.
Played with in Julian May's Saga of the Exiles. A time portal is created that can only send people back to a specific place around 6 million years ago. They attempt to avert this trope by banning the travel of any technology or psychic powers that could affect the future/present in any way, and forcing any women to be sterilised. However, it all goes a bit wrong when it turns out Earth of that time has been colonised by aliens from another galaxy, who can reverse the sterilisation and breed with humans (their Living Ship chose Earth specifically for that reason). Although the aliens have some advanced technology, they were largely living in a somewhat cleaner medieval society before humans arrived and started industrialising things. However, it turns out that even though sterilisation could be reversed and humans started breeding (with each other and the aliens), there were no alterations to the future. It's strongly implied that the aliens are responsible for Celtic mythology (despite most of the series taking place in France) and for humanity's strong psychic potential, but all traces of technology and civilisation were gone before the start of recorded history.
The Meddling Monk was planning this, talking about how Shakespeare would get to write for the TV.
In "The Time Warrior", Linx the Sontaran plans to give a medieval warlord firearms.
Star Trek: The Next Generation did this in the episode "A Matter of Time", where Berlinghoff Rasmussen, an "inventor" from the 22nd century, traveled to the future to steal technology which he could then reverse engineer and subsequently sell for profit.note Rasmussen stole his time machine from 26th century time travelers, but he didn't fully understand how it worked, which limited his ability to fully utilize it.
Star Trek: Voyager lifted this plot for the "Future's End" two-parter. A captain of a Time Ship from the 29th century gets stranded on Earth in the 1960s. A camping hippy finds the crash, and reverse engineers its technology to completely invent the Computer Age, draw out all the profits he can make from everything from the ship (and continually revolutionize his own revolutions) for as long as possible.
"A Private Little War". The Klingons are arming an Iron Age culture with increasingly sophisticated black powder muskets (rifled barrels were about to be introduced when Kirk and company intervene). The Federation responds in kind by similarly arming a different faction of that culture in a very anvilicious parable about the Cold War.
A similar thing happens in "A Piece of the Action": The inhabitants of an imitative culture get a book from a visiting starship, "Chicago Mobs of the '30s", and model their entire society around it. When McCoy discovers he's left his communicator behind, Kirk postulates that they may find it and remodel their society after Federation technology.
Alex does a fairly simplistic version in Ashes to Ashes, when in order to smoke out a suspect from several possibilities without arousing suspicion, she decides to (her words) "invent speed dating twenty years early".
Its predecessor series Life on Mars has this in abundance- Sam is always trying to introduce modern policing methods, apply his future knowledge and so on, much to the ire of Gene Hunt. As well as other non-police-related things (having a TV in a pub, chicken in a basket, etc.)
The time travel arc of Galactica 1980 is constructed about this. Realizing that Earth's technology would be insufficient to repel the Cylons were the Galacticans to reveal themselves to the earthmen, radical scientist Xavier researches Earth's past and decides that the best course of action to advance Earth's technology is to give the Nazis rocket technology which would allow them to win WWII. Fortunately the heroes have followed him to the past and thwart the attempt.
The same attempt is made in an episode of the short-lived Time Cop series, when a German yuppie travels to the 40s and introduces enhancements to Nazi technology. Slightly justified in that he had already done all the research he needs in order to improve their tech. When Logan goes back (again) to stop him, he walks into his lab, where a German scientist is trying to figure out how to work the yuppie's laptop. The Nazi is obviously having trouble with a concept such as a portable computer. Logan simply smashes the laptop and leaves. Of course, he leaves all the pieces in the past, which means there should still be a potential for reverse-engineering it.
An accidental example in Journeyman episode "The Hanged Man", when Dan accidentally leaves a digital camera in 1984. He goes to work at the newspaper and sees holographic screens and video-playing paper. It's all well and good until he also finds out that his son was never born because of a malfunction with the new systems at work when he was supposed to have sex with his wife. Instead, a daughter is conceived later. He ends up going back and stealing the camera (well, it's not really stealing, since the camera is his anyway) from a tech company in the process of studying its microchip.
In Misfits an old Jewish man goes back in time to kill Hitler. He fails and drops his mobile phone, which enables the Nazis to develop better technology and win the war, taking over Britain. Kelly gets the time travel power and is able to get the mobile away from Hitler, along with beating him up.
The Beverly Hillbillies is as close you can get to this without using time travel- seeing as the Clampetts lived like it was still the 19th century before becoming wealthy(one truck among them, horse travel still being common in their region, and one phone in a 40-mile radius being the most advanced they had it), the sudden culture shock of moving to a modern Beverly Hills mansion with all the modern furnishings allowed for some real oddities.
GURPS has included the rules for doing this since the first edition. And it happens fairly often in Infinite Worlds despite ISWAT's best efforts, though with alternate realities instead of the past or other planets.
Unscrupulous Traveller merchants can sell TL12 weapons to TL1 societies.
Might and Magic VII features a somewhat... complicated non-time travel version. One group aims to restore contact with the Ancients, which (since the loss of contact caused the fall into barbarism in the first place) could be seen as a roundabout way of getting someone better equipped than you to do this. The other group claims to have this as a goal for the Lost Colony you are on, and in a limited fashion does so in their (non-canonical) ending... but that might be more realizing that even with superior technology, you need an army to use that superior technology, lest you be swamped by the thousands of dragons and assorted powerful critters out there. Throwing things for a loop is that both factions themselves come from another primitive world, and have only gotten a better grasp on Ancient technology than the locals through the circumstances of them getting there.
This is essentially the whole plot of Time Shift. A scientist, Dr. Krone, steals a time travel suit his company had developed, disappearing into the past, and setting the building to explode to cover his tracks. The protagonist, another scientist, attempts to follow him in a less reliable prototype suit. He arrives in 1939, several years after Krone's destination, and he finds that the '30s look quite different than in the history books. Krone has leveraged his knowledge of future technology, using it to form a new, dictatorial government with himself at the helm. He's also fast tracked technological development, turning the '30s into a Steam PunkDystopia, complete with battle zeppelins and giant mechanical spiders.
The plot for World of Warcraft's fifth expansion, Warlords of Draenor, is kicked off by Garrosh going back in time 35 years to Draenor (the world the orcs come from) and introducing Azeroth's modern vaguely steampunk technology to the hunter-gatherer orcs.
In Cradleland, a man from twentieth century America had flown through a hyperspatial interstellar portal to a world populated by Transplanted Humans and got stranded there. He had patented a few inventions due to his technical knowledge, including a Stirling-cycle engine. He did not bring any radios though.
Rome, Sweet Rome examines whether a modern U.S. Marine Expeditionary Unit could overthrow the Roman Empire in the reign of Agustus (23 B.C.).
I have no illusions of raising this place to a 21st century standard of living, or even a 20th century one. I'm no Connecticut Yankee, just a Seattle Geek who happens to know a few things about the way things work. ... For example, I know that spinning a magnet around inside a coil of copper wire produces an electric current. But how strong of a magnet? How big does it have to be, and how fast does it have to spin, before you get anything useful? Does the size of the coil of wire relative to the magnet matter? Does the number of loops in the coil matter? We're rediscovering all these things from first principles.
Justice League: In "Savage Time", the immortal Vandal Savage sends a laptop with a message on it to his past self, the information on the laptop allowing the past Savage to take control of Nazi Germany and lead them to win World War II.
Invoked by Venger in an episode of the Dungeons & Dragons cartoon. Venger uses his magic to kidnap a jet-fighter pilot and his jet from the future, and a German WWII Luftwaffe pilot. His plan was to send the Luftwaffe pilot back to WWII with the futuristic jet, so Germany wins the war, preventing the birth of the heroes. Fortunately, his plan failed, because the German pilot pulled a Heel-Face Turn after meeting the heroes, who convinced him of not going along with the plan.
The Family Guy episode "Life of Brian" begins in a present day America ruled by the Native Americans thanks to Stewie traveling back in time and giving them automatic weapons.
Played straight in some cases of people discovering "isolated people" and the eventual giving of current technology... at least to a partial extent.
To disastrous results. Much of the famine in Africa in the 1980s was directly attributable to this. Much of the aid to Africa in the earlier parts of the 20th century involved bringing tractors to farmers who were, up until that point, still using wooden plows for their fields. Initially, the tractors boosted farmer productivity greatly, causing population booms as food became plentiful. However, since the aid did not include parts, gasoline, or technicians, the tractors over time broke down and the farmers had no means to repair them. Made worse by the gasoline crisis of the 1970s, which made the tractors too expensive to run, even if they were still operable.