When Galactus comes.... Everybody fights!
At the suggestion of a an unknown figure, Galactus is somehow convinced that the time is now to devour Earth.
To avoid any warnings, Galactus sends 4 of his Heralds (Thor, Fallen One, Terrax, and Firelord) to the Moon to distract Uatu with a fabricated problem.
While this occurs, Galactus sends Silver Surfer, Frankie Raye, and Korg to not announce his coming, but to immediately begin the destruction. Without a warning, heroes, villains, and civilians alike are quickly decimated. There is no mercy, the savageness of the destruction is horrifying.
Realizing they are woefully unprepared to save the Planet, what is left of the Illuminati (Dr Strange, Xavier, T'Challa, Namor, Iron Man) try to determine how many people can be saved and as importantly, where they can go.
While they do this, they send out the last group of surviving superpowers, a hodge podge of characters understanding a truce is needed to survive. They are loosely based as the last Avengers team, but most of the actual ones did not survive.
To help give the illuminati time: Captain America, Cable, Cyclops, Joe Fixit, Wonder Man, Archangel, Modok, Colossus, Juggernaut, Wolverine, Deadpool, multiple Spider-Men, Super Adaptoid, Vision, Warlock, and a reprogrammed Master Mold throw everything they have at the attackers.
Uatu finally realizes something is wrong as he is chased by the Heralds to Earth to join the final battle.
The illuminati finally find a safe haven and are able to save about 100,000 humans by Dr Strange opening a portal to their new home. As they realize time is running out and there is no hope of turning the tide, Dr Strange teleports the rest of the combatants as well.
From their new home, Captain America waits to speak with the Leader who accepted them in their time of need, still in disbelief that the Earth and billions of people died horrible deaths. Cap is then ushered in and is advised by the still unknown figure that there is a cost to being saved. Cap says he has no doubt that everyone is greatful and will do their share to help out. The mysterious figure laughs and explains that the cost for their rescue is freedom. Cap is then asked to bow his knee in servitude or they will be turned away. Exhausted, in great grief, and having the weight of the entire human race handcuffing him, Steve knows there will be time in the future to rebel and obeys.
The mysterious mastermind is then revealed to be the Supreme Intelligence!