The Legion of Superheroes part 1
The next thousand years of Earth-777 is a difficult one to talk about. However, the short version is that things got worse before they got better. The corporate greed, government corruption, societal apathy, environmental collapse, and mutant bigotry lead to a breakdown of society which the heroes were only able to mitigate rather than stop.
Megacorporations making use of alien and human-based technology seized control over large portions of the globe. Alchemax, Powers Industries, Stark-Fujikawa (led by "Evil Iron Man" Anton Stark), and Bain Enterprises divided the world between each other and a hundred other smaller superconglomerates.
How bad was it? Doctor Doom, or a time-lost variant of him, actually ended up becoming one of the biggest heroes of this time period because he had the 1% decency to believe leaving your subjects to starve in the street like animals was not cool. It was a time when Doom's Tywin Lannister-esque was considered a godsend.
The X-men managed to prevent their prophecized war between humans and mutants but, unfortunately, never quite achieved acceptance. The Sentinels were finally defeated by time-travelling heroes after they'd only taken over New York and a few other cities but the world grew quite sick of them. Many immigrated to the stars in hopes of finding a better life on worlds more accepting of the unusual.
Then something miraculous happened.
Things got better.
It was a slow process but new generations of heroes arose along with a gradual maturation of the human race. The inspiration of the 20th/21st century's heroes convinced many humans they could do better. The environment was repaired with the aid of Kryptonian and Rannian technology while a universal government based on the principles espoused by Kal-El of Krypton (now an elderly Science Council member) worked with the successors of folk like Commander America. Thor's descendant Magni, likewise, came to help change the world.
By the 30th century, Earth was unrecognizable. Mutants, humans, and (for a time) aliens were all accepted as equals. Reaching out to its lost colonies, Earth found thriving civilizations of superpowered humans from Titan (populated by telepaths as well as Eternals), Braal (where Magneto's genetic descendants had created a community of equals), and Winnath where all children were twins.
Earth found itself a near-Utopia and yet the galaxy around it was still dangerous. Annihilus' Wave had left the old empires utterly devastated and it was only now they had recovered. Ancient evils awaited on many worlds as humans moved to settle them. Super criminals formed indestructible syndicates that could take over whole planets.
In short, the universe didn't need a team of superheroes.
They needed a legion.