time travel thing.
I mean ... don't you think that a paradox was created by killing aliens in the past / present?
After all, the time travel that allowed Chris Prat's character to bring the toxin into the present to kill aliens could not have happened if the threat is annihilated in the past / present in the first place.
I'm not an expert and I could be wrong, but the only way this makes any sense is that Chris Pratt's character and his friends created an alternate universe where they stopped the invasion, Chris saved his daughter and also his own life (the car accident), but there must still be the original sad universe where all those bad things happened, even humanity's loss of the war.