Magneto's mutant city-island Genoshia was attacked by previously unheard-of giant robots. (The Sentinel plot, which'll probably happen in a few months, depending on game speed). The city was leveled and survivors scattered, but they're recollecting at the moment. Eric wants to warn Charles of what's coming, and is sending Raven to drop the information.
(Raven's history starts with XM:FC, left Charles and then a few decades of being Mystique and doing all her wicked things til up to date. This can be tweaked as you'd like their interaction, her history is very, pardon the pun, mutable.)