The Avengers are Earth's Mightiest Heroes, an appellation they've earned by facing the direst threats imaginable. Superheroes are magnets for trouble in a lot of ways, but some crises are worse than others. Sometimes, in Marvel's universe, cosmic-level threats show up out of the blue and need someone to stop them. Teams like the Avengers are a necessary bulwark against these events.

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The Avengers usually lead the charge against these kinds of threats, rallying the forces of Earth's heroes in order to save the day. It's never easy, but the Avengers and the heroes of the Earth have survived everything thrown at them so far.

10 Ultron Killed Millions And Destroyed Most Of Humanity In An Alternate Future

An image of Ultron fighting the Avengers, holding off Iron Man and Captain America in Marvel Comics

Ultron is the Avengers' greatest foe. Created by Hank Pym, the genocidal android has been trying to end all biological life for years now. Composed of unbreakable adamantium, Ultron is a nigh-unstoppable force of destruction and has personally killed millions of humans. He's always evolving and always a grave challenge for the Avengers.

In one terrible alternate future, Ultron made his most successful attack on humanity. His drones attacked everywhere at once and smashed through all opposition. The majority of humanity was destroyed, with only a time-traveling Wolverine and Sue Storm rescuing that reality with some trial and error.

9 The Apocalypse Twins Destroyed The Earth

The Apocalypse Twins in Marvel Comics.

The Apocalypse Twins are part of a venerable villainous legacy. The children of Archangel, when his Horseman of Death programming took complete control, they were taken by Kang as children. Each exposed to a Celestial Death Seed, they were kept in an alternate future's mutant concentration camp as a lesson from Kang.

Upon becoming adults, they broke away from Kang and attacked the Avengers Unity Squad, playing them against each other. They were able to manipulate the Celestials into doing their bidding by killing a Celestial with the Asgardian axe Jarnbjorn, making the Earth look dangerous to the space gods. The Earth was destroyed, only saved by a time travel Hail Mary from Havok and the Wasp.

8 Galactus Has Menaced The Earth Several Times

Galactus wields the Power Cosmic in Marvel Comics

The Avengers aren't on the front line of every threat. The first time Galactus came to Earth, The Watcher warned The Fantastic Four about the World Devourer's approach and they were able to get their hands on the Ultimate Nullifier. They threatened Galactus with universal destruction, driving him away from the planet.

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Galactus did return after to eat the Earth and that time, the Avengers did have a stake in the conflict. Galactus was in a starved, weakened state and the heroes of New York City, including the Avengers, attacked. It was the only time martial strength was able to defeat Galactus. Even then, the Avengers were only a small part of the overall victory.

7 Scarlet Witch Endangered The Earth More Than Anyone Knew

Scarlet Witch during House of M

Scarlet Witch is a beloved Avenger, but an argument can be made that she's irredeemable. Scarlet Witch has attacked the team multiple times over the years, her extreme power levels and tragic life reaping terrible results multiple times. Wanda can't seem to handle her godlike power and she's threatened her world multiple times as a result.

Scarlet Witch's power allowed her to remake the Earth, creating a world where mutants were dominant before erasing it all and depowering mutants in a fit of pique. Her actions have caused countless deaths, and she's been easily manipulated over the years, falling for ploys from Doctor Doom and the Apocalypse Twins.

6 The War Against The Builders Almost Destroyed The Entire Universe

The ancient race of Builders from Marvel Infinity

The Builders are the oldest race in the universe. Responsible for everything from seeding worlds with life to ordering space and time, they eventually decided to destroy everything in the face of the Incursions. The Builders sent their armies of Alephs and Gardeners out to destroy every life form in the universe.

The Avengers took an active role in fighting The Builders, traveling into space and helping lead the coalition of intergalactic civilizations in the war against the Builders. It was a desperate battle, but in the end, the Builders were defeated.

5 The Phoenix Force Has Almost Destroyed The Earth More Than Once

The Phoenix Force burns in Marvel Comics

The Phoenix Force is the personification of death and rebirth. First drawn to Earth by the X-Men's Jean Grey, it effectively possessed her. Driven wild by human emotions and the manipulations of Mastermind, it destroyed an inhabited solar system before turning its attention back to Earth. The X-Men stopped it and killed its Jean Grey form before it could devour the planet.

The X-Men mostly deal with the Phoenix, although eventually the Avengers had to battle it and a faction of X-Men led by Cyclops. The Phoenix's power is often too great for its hosts, making it quite dangerous every time it shows up on Earth.

4 The Magus Outfoxed Everyone And Got The Full Power Of The Infinity Gauntlet

Magus and Adam Warlock fight in Marvel Comics

The Magus was the personification of Adam Warlock's dark side, expelled after the hero received the Infinity Gauntlet. Eventually, the Magus would make his own attack on the universe in the vastly underrated Infinity War. The Magus was able to out plan everyone, from Earth's heroes to Warlock, his Infinity Watch. Even Thanos, Galactus, Eternity, and the Living Tribunal became pawns in the Magus' cosmic scheme.

The Avengers were little more than cannon fodder in the battle against the Magus and his forces, tentacled monsters that were twisted doppelgängers of the heroes. In the end, Warlock was able to win this battle, and the Magus was defeated before he could reorder creation how he saw fit.

3 The Beyonder's Power Dwarfed Gods

Spider-Man and Marvel's heroes battle The Beyonder in Marvel's Secret Wars

The Beyonder proved to be an extremely dangerous foe for the Avengers. The first time the heroes of Earth faced him, he was a disembodied force that pitted the heroes against the villains on a distant world. On that occasion, Doom stole the mysterious being's power, threatening reality. The next time the Beyonder showed up, he took human form and tried to learn as much about humanity as possible.

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Human emotion proved to be too much for The Beyonder, however, leading to erratic behavior. The Avengers did their best against him, but in the end, it was up to the usually villainous Molecule Man to defeat him. The Beyonder has returned several times since then but almost never with the kind of power he displayed in the first two Secret Wars series.

2 Thanos Devastated The Universe When He Had The Infinity Gauntlet

Thanos Looming Large With The Infinity Gauntlet, surrounded by foes in Marvel Comics

Infinity Gauntlet is the blueprint for many of Marvel's best events. The book's biggest achievement was making Thanos a big deal again. Thanos was always obsessed with genocide and gaining the Infinity Gauntlet made universal murder a lot easier. He caused widespread devastation, killing half the universe and wrecking continents on planets across the universe.

Many of the Avengers died before the battle against Thanos ever began, with only Captain America, Scarlet Witch, Thor, and Iron Man in the final fight. The team didn't play a very big role in this victory, although Thor was one of the few to survive every fight in the conflict.

1 The Incursions Destroyed The Multiverse

The Avengers surrounding an Incursion, their backs turned in shame, in Marvel Comics

2015's Secret Wars is an amazing event, but the build-up to it revealed Marvel's greatest threat to the Earth. The Illuminati, back together again, discovered the Incursions. These catastrophes were quite simple. An alternate universe's Earth would collide with another Earth, destroying both. The group came up with a way to save their world but only by destroying the others.

Time started to run out and finally, there were only two realities left, the Earth of the 616 universe and the 1610 variant. Both worlds were destroyed in the final Incursion. Only Doctor Doom was able to save what was left of creation by stealing the powers of both the Beyonders and Molecule Man.

Faced with the Incursion, the Avengers completely failed to save even a single Earth.

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