Alternate versions of Superman often dramatically shift the political climate of the entire Earth:
In Superman: Red Son, he becomes Premier of the USSR and takes over the world. After Superman decides he shouldn't be in charge, he fakes his own death, Lex Luthor becomes President of the US, takes over the world, and creates a One World Order that lasts for millions of years.
The original Silver Age Superman Red / Superman Blue story had the twin Supermen turn the world into a utopia. It's a pretty weird story, even by Silver Age standards.
In pre-Crisis stories, Lex Luthor once had a Pet the Dog moment where he saved the civilization of an alien planet. The locals idolized him for it (renaming their planet "Lexor"), and Lex decided he liked being seen as a hero somewhere, so he kept on doing nice things for the locals for years, even marrying a Lexorian woman. Then the planet was destroyed during a battle with Superman who'd traveled there in order to take him back to Earth.
The Superman of Earth-23. "Now, disguised as United States President Calvin Ellis, Kalel of Krypton fights a never-ending battle for truth, justice, and the American way as... SUPERMAN!" No Forty-Fourth Presidents Were Harmed is in full effect. For bonus points, he's aided in his global peacekeeping efforts by a reformed version of Brainiac, who can use his advanced Coluan technology to resolve political crises in seconds.
In Superman: Space Age, Superman eventually puts his super-intelligence to work to cure every disease on the planet and transfer most of humanity's DNA signatures to another universe where that universe’s Superman can use them to restart humanity on that universe's Earth.
The JLA/Planetarycrossover "Terra Occulta" is set in an alternate universe from both directions (that is, it's neither the usual DC Universe nor the usual Wildstorm-verse). Technological and social changes caused by the existence of superheroes are everywhere, although it's clear that Planetary are withholding most of the good stuff and have killed off most of that universe's metabeings to obtain it. They've essentially become that universe's version of The Four (the Big Bad of the mainstream Planetary universe). It should be mentioned that "The Four" in the main Planetary/Wildstorm setting are evilexpies of the Fantastic Four.
In Flashpoint (1999), while Barry's body was ruined, his mind still worked at super speed, and he managed to accelerate the space program to the point where humans successfully landed on Mars.
In Ultimate Fantastic Four, when Ben goes back in time to avoid being turned into the Thing, he changes time such that Reed and the Skrulls modernize the world even more and give everyone superpowers. It does not end well, but only because of the Batman Gambit of the Token Evil Diplomat.
Later in this continuity he works for a government think-tank, but eventually gets so frustrated at not being able to change the world for the better in this position that he decides to MAKE things change. By force.He's since conquered most of Europe, destroyed Washington, D.C., killed nearly all the Asgardians, and now rules a nation notably more powerful than the United States. Until he was stopped by a sentient tumor.
In Earth X, his attempt at free power through Vibranium reactors mutates the whole world. Except it was actually a Terrigen Mist bomb set off by Black Bolt.
In the possible future of Fantastic Four: The End, Reed has turned the world into a technological utopia.
The "Solve Everything" story arc features an alliance of alternate-universe Reeds, aptly named the Council of Reeds, who have ended famine by turning entire planets into super-productive farms, among other things. However, they've also eliminated dozens of worlds' Doctor Dooms by lobotomising them and turning them into slaves. This story arc makes it clear that the reason the main Reed is "useless", is because he cares about his family more than all those other "awesome" Reeds; however, the alternate Reeds are entirely defined by their work, and have all lost touch with their humanity.
In the FF part of the "Forever" arc (a continuation of the story that began in "Solve Everything"), the same alternate-universe Reeds who never established the loving family life with Sue Storm that keeps "our" Reed grounded and sane reappear. The evil alternate Reeds are so powerful that 616 Reed has to call in all his main enemies for help in taking them down.
Also subverted in another Alternate Universe where Reed Richards acquired the abilities of the Thing as opposed to Ben Grimm. Because of this, he became reclusive due to his freakish appearance. In fact, the Ben of that universe ended up marrying Sue Storm, instead of him. When Reed Richards of the normal 616 universe met him and asked for his help (see the above points), this version of Reed agreed but quickly told him to leave soon after. This was because, not only did the 616 version look human but he also married Sue. The Thing-Reed warned that he could go into a rage at any moment due to jealousy.
Exiles has featured numerous Reeds, most of them pretty badass. Two particularly good ones include a rebel resistance fighter against the evil ruler of his Earth (an evil Invisible Woman), and a former gladiator who builds a device that forces a fully powered Galactus to flee.
During Reckoning War, Uatu is forced to view a world where he didn’t interfere with Galactus’ arrival. While the Fantastic Four are maimed, Galactus is destroyed, peace comes to Earth and Reed ushers in a new power source. Uatu is horrified to learn what he had prevented, but Nick Fury, Sr. reveals more to that story: that the power source would go critical and destroy the world, thus absolving Uatu of his decision.
Speaking of Civil War (2006), Reed once looked at other universes in order to see if he could've done something differently. Many of the realities he saw showed that the Civil War was averted. Mainly, the reason why the 616 universe one ended as badly as it did is that Reed Richards did it all himself in the other realities. In the 616 universe, he worked alongside Tony Stark and Hank Pym. Though one of those universes that had no Civil War and was a utopic one was due to the efforts of Steve Rogers and his wife ''Natasha'' Stark. Not kidding.
This is actually part of the justification for why Doctor Doom is dead-set on world domination. Doom used his time machine to look into alternate timelines, and the only universe he found that was completely free of poverty and want was the universe where he ruled over it. This convinced him that he needed to follow through on his own world.
This gets deconstructed in a solo series where he travels to such a universe. He finds that Doom managed to usher in a utopia by eschewing his ego and working with other great minds to improve the world. The fact that he would even do this with Reed Richards, plus being mocked for his petty vanity, causes Doom to obliterate that universe.
In Supreme Power the resident super genius' inventions ultimately backfire and worsen the world.
In the original version, the Squadron Supreme who were Expies of the Justice League of America, their resident genius Tom Thumb invented cryogenic stasis, behavior modification devices to turn criminals into good people, pacifier guns that overwhelmed a target with pleasure, personal force fields which could shrug off gun fire. These were all mass produced for either civilian use or local law enforcement.
In the 616 universe, Mimic is a largely forgotten footnote. The alternate universe version who starred in Exiles was a leader of the X-Men and one of his world’s leading superheroes, beloved celebrity, friend to every major hero on earth and multiversal adventurer. In fact, his whole universe seems to have been this, a near-utopia where every superhero was the best possible version of themselves. Ironically, the reappearances 616 Mimic has made in recent years are probably off the strength of Exiles Mimic significantly raising the character’s profile.
On a parallel world ravaged by a mutated Legacy Virus which the Exiles visited several times, Hank Pym, one of Marvel’s biggest Scrappies/Butt Monkies, was the Badass NormalScience Hero leader of the Avengers and protector of the last uninflected human city.
Thanks to Joker Immunity, The Punisher can't ever kill scum like The Kingpin, or even really curb crime significantly. However, in one "What If?" he manages to take out every super villain... and every superhero... in Marvel. The circumstances were that his family was killed in the crossfire of a fight between supers and an alien race.
The Marvel MAX series possibly counts as well. Some arcs have introduced both Kingpin and Bullseye, both who end up dead. Along with Frank, apparently.
In "What If? The Punisher received the Venom symbiote", the Punisher kills the Kingpin too. However, upon realising that the symbiote was controlling him (blackouts, attacking allies, trying to kill Spider-Man etc), he tells it that if he won't be in control, he'd rather die and take the symbiote with him. The symbiote backs down, and the Watcher of that universe states that the Punisher actually got control over it.
There was an alternate universe version of Ben Grimm who traveled back in time, became a pirate (named Thingbeard), singlehandedly defeated the British Empire, and founded the United States of America. He did that in the 616 universe as well. Except for the bit where Deadpool buggered up his travelling Back to the Future bit.
What If? v2 #64, written by Simon Furman, featured Tony Stark, upon first inventing the Iron Man suit, make his technology available to governments around the world. This has many positive effects, especially in health care; unfortunately, it has many negative effects as well, as despite his best efforts, governments used it in arms races; and despite their best efforts, the tech filtered out to supervillains, who used it in arms races of their own. Years down the line, most non-armor based heroes and villains were made obsolete, an enhanced Doctor Doom killed the Fantastic Four, and Magneto declared that if the world's governments didn't back off from their use of Stark-tech—as it was being used to persecute mutants—he was going to start wreaking havoc on an unprecedented scale. Stark attempted to capture Magneto and use him to generate a worldwide electromagnetic pulse to shut down all technology, both his own and otherwise, in a last-ditch attempt to undo the harm he'd unwillingly caused; however, his best friend Jim Rhodes talked him out of it by reminding him of all the good Stark-tech had done and could still do. Stark chooses to Take a Third Option, using the threat of the Magneto pulse to blackmail the world's governments to stop using his technology for offensive purposes.
In What If? #33, "What if Iron Man had been trapped in King Arthur's time?", he ends up having to repair his armor, which he does by (starting with a medieval forge) using "crude tools to fashion better tools". He eventually succeeds King Arthur, making sure Camelot never falls, and kicking off the Industrial Revolution... in the 8th century.
One Captain America story arc showed an alternate history where the Axis had won World War II and Red Skull had succeeded Hitler as Fuehrer. As a technology enthusiast, the Skull employed most of the Marvel supergeniuses (among others, Tony Stark and Doctor Doom) as science advisors, and used their Super Science to change the world. By the 1960s, supersonic airliners, maglev trains and flatscreen TV monitors were commonplaces, and the Gestapo's advanced surveillance and intervention technologies included GPS tracers and powered-armor SWAT teams based on the original Iron Man design.
In Spider-Man: Life Story, we see a world where our heroes age in real time and we see Peter Parker working with Reed Richards and a reformed Otto Octavius in the Future Foundation, where they create wondrous stuff for humanity. However, we end up finding out that Reed Richards Is Useless is in effect here as well as Reed withholds the most advanced stuff due to the fear of superhumans taking over the world (and seeing as, by the 70s, mutantkind is on the rise, the fear seems justified.)
Generally subverted by Cyclops. Scott tends not to fare well in parallel universes, typically ending up evil or dead or evil and dead or just shunted aside to allow a more marketable character the spotlight. You can play a drinking game reading the original run of Exiles: sip your drink every time he appears without dialogue, take a shot every time somebody else is the leader of the X-Men, take two every time he dies. You’ll be blind drunk by the time Hyperion shows up.
Tyler gets to peek into his alternate selves' minds while visiting the Castle Beyond Time and Space. The three we see all have superpowers, and one is basically worshiped as a god in his world, though interestingly, that one predicts that Prime!Tyler will be the most important one of them all.
