I like how humanity turns barbaric - it seems realistic... The start, though - humanity being attacked by AI - reminds me strongly of the Quarians and Geth in the Mass Effect series (and of the Terminator series, and certain Asimov works, etc). Wrongu and I came up with a slightly different version where it's the other way around - humanity is enslaved by an AI (or aliens) for as long as they can remember. Eventually a group manages to escape and begins to build colonies and computer technology back to where it had previously been.
Yours works, really, on initial analysis... We'd still need a reason to wipe out Earth, as we don't want to include it in the game, as far as I know... I'm also pretty sure we want to include some sort of "major enemy". Apart from the admittedly cliche "robots turning on us" theme, it seems to work. I'm not totally against it myself, but I'd want to come up with some way to make it a little more unique.
From a writing perspective, it would be difficult to build any compelling lore substories off of yours, too, come to think of it, as all knowledge is lost when the war is ended.