In the war between human and machines, why didn't the machines just leave Earth behind? The technology at that point was sufficient for machines to exist in space and since it's never been mentioned that humans were actively exploring space, why not go where they wouldn't be bothered? Really, they could head around in just about any direction since they wouldn't be limited to Earth-like worlds, assuming they wanted to exist on a planet which they don't need to do. In space they could mine asteroids or planets for any materials they need. They could build huge solar power complexes giving them all the power they need. Why stick on a piddly ruined little planet subsisting on human energy by-products and all the problems that go along with it?