The heroes begin to wonder what’s happening as some heroes are remembered while others aren’t on this Earth, and why weren’t Superman [Earth-2] and Flash [Jay Garrick], as well as other heroes not able to return back to their respective worlds after the battle at the dawn of time.
For example, at Titans Tower, Wonder Girl tells of how Queen Hippolyta reacted when the Earth-Two Wonder Woman and her daughter Fury appeared on Paradise Island. None of the Amazons remembered the Multiverse, even though the “new” Paradise Island had elements from both Earths.
Harbinger then explains the multiverse is no more as a result of that battle, as a single universe is now in existence with aspects from each surviving world. The Antimonitor later appears to try and finish what he started as he pulls the single Earth into the antimatter universe.