UFO: Afterlight

In Aftermath, the few human survivors of an alien attack were forced into a devil's deal to preserve their race and abandoned the Earth's surface to the invaders. In return, some of humanity was moved off-planet to orbital colonies and to a small Mars colony. Aftershock features the subsequent events on Earth a half-century later while Afterlight focuses on the hitherto ignored inhabitants of Mars concurrently with Aftershock.