This timeline is created when Legion, Xavier´s son, goes back in time in an attempt to kill Magneto. Legion fails and erroneously kills Professor Xavier (See Legion Quest). Apocalypse is able to see that his time has come to bring his sort of order to the world. (See the Age of Apocalypse story arc). The disbalance created by this world threatened the Marvel Multiverse so the X-Men of this reality starts the final confrontation against Apocalypse forces.
The X-Men managed to destroy Apocalypse and stop the realities´ shattering, although it seemed that this reality would disapear this alternate Earth continues after nuclear armagedon. Then humans and mutants join forces to rebuild their world.