A powerful new team of heroes called the Eternals will be joining the Marvel Cinematic Universe, though they have had a bit of a controversial arrival. Trailers first revealed that the Eternals were powerful aliens created by Celestials that had been sent to Earth thousands of years ago to defend it from the monstrous Deviants.
The Eternals promised not to interfere in humanity's development and separated to live hidden lives, though they returned after the events of Avengers: Endgame. There are a few huge MCU threats like Thanos that the Avengers could have used some help with if the Eternals hadn't hidden away from a number of major events.
10 Thanos Is One Of The Deviants The Eternals Are Sworn To Fight
It makes sense that the Eternals would be motivated into reforming after Thanos gathered the Infinity Stones together and decimated the universe's population with a single snap. Not only was it a devastating event that could have even threatened them, but Thanos is one of the very beings they were supposed to fight against on Earth.
While it isn't explored much in the MCU, Thanos is also an Eternal from Titan— though he was born with a Deviant gene. That makes the Eternals partially responsible for everything Thanos did, as they failed in their sworn mission against the Deviants.
9 Red Skull & HYDRA Almost Changed The Outcome Of World War II
There were Eternals hidden across the globe for centuries, which means they lived through humanity's wars as well as the biggest superhero events of the MCU— which combined during the Second World War. 2011's Captain America: The First Avenger introduced the powerful Red Skull and the beginnings of the HYDRA organization.
They threatened to take over Europe and then the world using advanced tech derived from the Tesseract/Space Stone. While Captain America was able to stop Red Skull's plans, the Eternals' involvement with the allied forces (like most comic book superheroes of that era) would have helped save a lot of lives.
8 The Kree Would Have Annihilated Earth But Captain Marvel Saved The Day
2019's Captain Marvel took place in the 1990s and explored the Kree-influenced origins of Carol Danvers that led to her debut as one of the MCU's most powerful heroes. After spending some time with the Kree Starforce, she arrived on Earth and discovered the truth about her past and the Kree Empire's lies about the the alien Skrulls.
Earth became a target by the Kree's army of Accusers led by Ronan who brought an armada of ships into Earth's orbit that would probably be easily detectable by other aliens like the Eternals. If Captain Marvel hadn't driven the Kree away, Earth and the Eternals could have very easily been annihilated before Nick Fury even finalized his plans for the Avengers.
7 Loki's Invasion Of New York Would Have Unleashed The Chitauri On Earth
Thanos's earliest move against Earth involved powerful pawns like Loki who he outfitted with a scepter that contained the Mind Stone. Loki was also given a powerful alien army known as the Chitauri that he attempted to bring to Earth in 2012's The Avengers.
The Avengers were pushed to the limit in their efforts to repel the alien invaders, stop Loki, and protect New York City from an attack by its own government. Loki's attack took place worldwide and would have received attention even before the alien invasion, which could have brought the Eternals together a bit sooner to try and help stop the seemingly evil Asgardian.
6 Malekith The Dark Elf Threatened To Shroud The Universe In Darkness
While a lot of Thor's adventures happened away from Earth, 2013's Thor: The Dark World introduced Malekith the Dark Elf and his armies. Alongside the powerful Kurse, Malekith attempted to gain the power of the Aether/Reality Stone during a time of cosmic Convergence that brought the nine realms together.
While the Eternals wouldn't have had much of a warning about Malektih's plans, the portals opened by the Convergence spread across Earth and the Nine Realms. The Eternals could have not only been aware of the cosmic event already but been alerted by the armies of Dark Elves and even Asgardian creatures that came through the portals.
5 Ultron Invaded An Entire City & Threatened To Exterminate Humanity
2015's Avengers: Age of Ultron introduced the deadly artificial intelligence known as Ultron who was created by Tony Stark and Bruce Banner using research from the Infinity Stones. Ulton's plans to protect humanity from itself began with internet hacks and continued with broad daylight attacks against the Avengers that led to the destruction of some of Seoul in South Korea.
The Eternals would likely have been quite aware of Ultron and his attacks by the time he went after Slovenia and attempted to create an extinction event, and the Avengers definitely could have used help to reduce the loss of lives during yet another tragic destruction of a city.
4 Kaecilius Almost Brought Dormammu & His Dark Dimension To Earth
A group of highly-trained mystical warriors led by Kaecilius first appeared in 2016's Doctor Strange as they turned against their teacher, the Ancient One. Kaecilius destroyed the majority of the Sanctum Sanctorum's that protected Earth from other-dimensional threats. He almost succeeded in his attempt to bring the powerful entity known as Dormammu to Earth.
He planned to spread his Dark Dimension further, which would have greatly impacted the Eternals. It might have been too late for them to help if Doctor Strange hadn't been able to trick Dormammu, but earlier intervention by the Eternals at any time before this event could have made it easier for them to help protect the Sanctums.
3 The Eternals Might Have Been Able To Keep The Avengers From Civil War
The MCU hasn't just been threatened by powerful cosmic beings over the years, as 2016's Captain America: Civil War showcased. Baron Zemo was able to manipulate a divide between Earth's Mightiest Heroes that allowed him to also create political unrest across the world.
If the Eternals had been present in the events of the world they might have been able to provide a voice of reason to the Avengers. The Eternals could have used their accumulated centuries of wisdom to help see through Zemo's ploys and help keep the Avengers together in order to better keep the Earth safe when Thanos finally arrived.
2 Ego Almost Expanded & Transformed Earth Into A Living Planet
One of the biggest cosmic events that threatened numerous planets was the expansion of Ego that occurred in 2017's Guardians of the Galaxy Vol. 2. Peter Quill/Star-Lord found his real father, who was the Celestial being that was eventually revealed as Ego the Living Planet. Ego planted his seed on different planets— including Earth— hoping to spread his consciousness and take over.
The actual expansion on Earth was triggered, but not much was shown about the local hero's reaction to the devastating alien growth. Star-Lord and the Guardians were able to defeat him, but the Eternals would have been forced into action early if they didn't.
1 Mysterio Attacked Cities Across Europe With His Elemental Monsters
Another MCU threat whose attacks spread across different countries and would have definitely alerted the Eternals was Mysterio from 2019's Spider-Man: Far From Home. The revenge-fueled scientist was able to create powerful holographic illusions of monstrous Elementals that he claimed were from an alternate reality.
Spider-Man was able to figure out his tricks and ultimately defeat the villain at the cost of his secret identity. However, given the European locations of the attacks and the global reach of the news, the Eternals could have greatly assisted Spider-Man in dealing with Mysterio had they decided to reform just a little sooner.