Halo 3

Master Chief returns to a Covenant Dominated Earth on a mission to kill the final alien leader. Meanwhile, the Arbiter, Johnson, and Keyes form a loose alliance and escape from Delta Halo. The Covenant is ripped in civil war, and the Elites along with a handful of other alien races become sympathetic to the human cause. Delta Halo's impromptu dis-activation has brought all of the Halos to a "remote activation phase". They can be activated from a facility called the ark, which happens to be on Earth.

See more info at these sites by clicking:

Google	Google Images	Youtube	Wikipedia