IIRC the robots have won against humanity, but then the robots started to fight among themselves for resources. The player is one of those robots who has some sort of amnesia.
Well, this matters as much as the details of the trees in a racing game, in my view.
(I'm not exactly sure what the current official lore is - at some point it has been added to the campaign though, but also of note : both TA faction have been compressed into one and then split into 11+1+1 factories for gameplay reasons.)
I feel like such a pedantic nerd asking this, but the debate over people vs. sentient robots was the whole reason for the war!