When What If...? premieres on Disney+ in August, fans might not know what to expect. The idea behind the show is to examine a key moment in a past Marvel movie and then ask, "What if something different happened that changed everything about that movie?" In a trailer for the series, this exploration of alternate realities was vividly brought to life in a scene from a Marvel Zombies-inspired episode that depicted the destruction of the Marvel Universe.

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The Marvel Zombies story wasn't even from the actual What If...? comics, but it is a good look at what happens when things change in Marvel for the worse, a theme that reoccurs throughout the comic book series. When looking at past issues of What If...?, which debuted in 1977 and is still going today, there are plenty of times that changing one moment in a past storyline destroyed the entire Marvel Universe.

What If Korvac Beats The Avengers?

Korvac fighting the Avengers.

"The Korvac Saga" occurred in The Avengers #170-177 and focused on Korvac, an extremely powerful man from an alternate Earth with the power to manipulate and change reality to any form he wishes. Korvac traveled from his world to the main Earth and hid for years, hoping to change things to make it a "better place." While The Avengers died fighting Korvac, he realized the error of his ways, brought them all back to life, and left their world.

In What If...?, Korvac continues to create his perfect world by banning the gods and eliminating Marvel's most powerful heroes. He was defeated when he used the Ultimate Nullifier and destroyed the entire universe.

What If Dark Phoenix Lived?

The Dark Phoenix destroys the Earth.

One of the most popular What If...? storylines in history was "What If the Phoenix Had Not Died?" in 1981 by Mary Jo Duffy and Jerry Bingham. This story was inspired by the legendary Uncanny X-Men storyline "The Dark Phoenix Saga," where the Shi'ar Empire put Jean Grey on trial for murder and she sacrificed her life to stop the Dark Phoenix.

What If...? had Jean Grey as Phoenix stop Galactus and save the Shi'ar Galaxy, sparing her from the trial. However, because she never sacrificed herself to stop the Dark Phoenix, the celestial being grew in power. She ended up killing all her closest friends, from her lover Cyclops to her best friend Storm, before destroying the entire planet.

What If Wolverine Fought Conan?

Wolverine fights against Conan

Wolverine and Conan the Barbarian are currently members of the Savage Avengers in the Marvel Universe and have one of the strangest friendships in Wolverine's comics. But before he joined the Savage Avengers, Conan belonged to a different Earth and had no connection to Wolverine. In the What If...? comic series, the two men meet for the first time.

This meeting took place during the "Dark Phoenix Saga" and had Wolverine accidentally discover the Watcher's base and end up falling into a portal to Conan's world. The two men fought and Conan accidentally ended up in the main Marvel Universe. Conan then attacked the X-Men, which caused the Dark Phoenix to awaken and destroy the Earth. Wolverine was miraculously spared and lived out his life on Conan's alternate Earth.

What If Cable Killed The X-Men?

Cable pulling his guns on the X-Men.

Cable showed up in the Marvel Universe from a post-apocalyptic future where humanity hunted mutants and ended up destroying the entire world because of their fears. Cable wanted to stop this from happening and became an ally to the X-Men and his father Cyclops.

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What If...? showed Cable taking the other option. He used a bomb to kill Professor X, Cyclops, and Jean Grey, and then the rest of the X-Men fell without their leaders. Magneto then took control of the government, which caused the Sentinels to defend humanity with a nuclear attack that ultimately destroyed the world.

What If All Humanity Became Snakes?

Captain America and Wonder Man fighting giant snakes.

The 1989 event series Atlantis Attacks had Earth's heroes trying to stop a plan to bring the demon god Set to Earth to conquer the planet. The heroes won this battle, but in a What If...? issue, the heroes lost and Set was triumphant.

In this alternate reality story, Namor died early and both the Punisher and Moon Knight failed in their mission to stop the spread of a drug that turned humans into snakes. While the entire world ended up turning into snake people, Set had his bride deliver babies. When those children were born, they then consumed everyone on Earth and left the world dead.

What If Annihilus Reached Earth?

Wolverine and Spider-Man battles Annihilus.

The Annihilation Wave destroyed everything in its path in Marvel Comics. This was a 2006 Marvel Comics crossover event that took place in the far reaches of space and saw Nova, Silver Surfer, the Skrulls, and Kree all battle to stop the Fantastic Four villain Annihilus.

What If...? saw the Annihilation Wave reach Earth at the same time the Civil War storyline was raging. Because the heroes were fighting each other, they were not prepared for the attack. Annihilus reached Earth and killed a massive amount of heroes and villains. Captain America, Nova, and Iron Man finally sacrificed their lives to save Earth, which was transformed into a post-apocalyptic wasteland.

What If Hulk Won In World War Hulk?

Hulk vs the world in World War Hulk.

World War Hulk took place in 2007 and followed the popular Planet Hulk storyline. In Planet Hulk, the Illuminati, a secret team of Marvel's most important heroes, tricked Hulk and banished him from Earth, sending him to a planet where ended up marrying an alien. After an explosion killed his pregnant wife, a vengeful Hulk returns to Earth in World War Hulk and briefly fights with his former superhero friends before surrendering.

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What If...? had Hulk win against Earth's heroes. With Marvel's mightiest incapacitated, the Skrulls seized the opportunity and killed all the heroes. This story ends with Hulk sending for Galactus, who appears and consumes Earth before making Hulk his new herald, one of the most powerful versions of Hulk.

What If Hulk Died In Planet Hulk?

Hulk's wife conquers Earth and beats Iron Man.

What If...? had a second World War Hulk story, but changed things up this time to take Hulk out of the event completely. In this story, instead of Hulk's pregnant wife Calera dying in the explosion, it was Hulk who died. With her husband dead, Calera gathers a group to attack Earth to seek revenge. She showed no mercy, and unlike Hulk, she killed everyone, including the entire Inhumans race on the moon. She also killed Doctor Strange, Sentry, and Iron Man, before she took over Earth and enslaved the remaining heroes, building a monument to honor Hulk.

What If Norman Osborn Won Siege?

Iron Man on the cover of What If Siege.

After the Skrulls attacked Earth in Secret Invasion, Norman Osborn was in the right place at the right time. He assassinated the Skrull Queen and became a national hero overnight. Osborn took the opportunity to take over S.H.I.E.L.D. and then built his own Dark Avengers team. Osborn's brief time as an antihero ended when he attacked Asgard in the Siege storyline and lost.

What If...? showed what would have happened if Osborn won the Siege event. Norman released Sentry to achieve his goal of conquering Asgard. Sentry then began killing almost everyone in his path, from the X-Men and Avengers to the Fantastic Four. Even Norman Osborn died as Sentry destroyed the entire Marvel Universe.

What If The Skrulls Won Secret Invasion?

The Skrulls attacking in Secret Invasion.

Secret Invasion saw the Skrulls attack Earth after a long-planned invasion where they had begun kidnapping and replacing humans with duplicates. They would have won too, if not for Norman Osborn killing the Skrull Queen when she least expected it. Secret Invasion could drastically change the MCU, but it could have done more in the comics if the Skrulls had won.

In What If...The Skrulls Succeeded In Their Secret Invasion?, the Skrulls won and offered all humans a chance to become Skrull converts. Wakanda found a way to kill all the Skrull hybrids, but Norman Osborn became a Skrull convert and sabotaged the virus, killing billions of humans instead of the Skrulls.

NEXT: Marvel's What If?: 10 Things We Learned From The Trailer