>>86087461They can't go back before the EDF was created because then they wouldn't have a reason to go back in time, creating a time paradox.
EDF (you and scientist) go back in time by hijacking the loop from the aliens after they loop back by damaging their time machine, this happens several times. You go back to the various stages in EDF 5, all the way to the tutorial. So still after EDF was formed.
In the end, the humans decide to nuke Mars so that no life could ever develop there, however, they would only do it if the Aliens came back to invade Earth in the first place, so now you have two time paradoxes battling it out and this battle is settled by the fight between you and the combination of every alien in every time, the loser being erased from time.
