"Yeah," Gordon says. "They've had control of the planet ever since. What they don't hold outright is pretty much uninhabitable, since it's been overrun by alien wildlife. Like those headcrabs." He shakes his head, but slows his passage; there's light up ahead, and he has to be careful. "Anybody who angers the Combine gets 'disappeared'. Anybody who serves them willingly gets 'promoted' through cybernetics and massive mental and physical modification. And if a whole community pisses them off, the Combine starts loading headcrabs into rockets and shelling the living daylights out of the place, and it winds up just like here."