The Covenant has returned in Halo 4 but a lot of things about it are unclear. How did they get to this planet? Were they already here or did the just recently find it? Why are they here and where have they been, if not fighting against humanity?
Not a lot is known about what is left of the Covenant after the war against them. Some groups have clearly survived while we are unsure of others. It also appears that at least a portion of the Sangheili (Elites) are present as part of the Covenant forces. With Brutes not appearing and the Elites seeming to be in a leadership role, the possibility of these Covenant forces simply being stranded and possibly even nearly feral can't be ruled out.
