In the 2015 version of the event, the heroes of the world deal with the Incursions, multiversal events in which various alternate universes are beginning to collapse on each other and collide, causing multiversal destruction. Our heroes are trying to prevent these Incursions from happening to their world.
However, they fail to stop the destruction of their own reality, as their Earth as well as the entire multiverse is destroyed.
Doctor Doom manages to steal the power of the Beyonders (cosmic beings) and becomes a god-like being, reforming the various universes into a single world under his command called Battleworld.
He is God Emperor and the various universes are divided into different territories, all of whom have forgotten their past lives and think Doom created the universe. The few who remember include Doctor Strange, who is now Doom’s sheriff and has no choice but to serve, and Molecule Man, who is helping Doom keep control.
However, some from the main Earth manage to survive the Incursion and remember their past, and the story is them trying to bring back their world and take down Doom.