The Uncanny X-Men: Days of Future Past

For the X-Men, the future is history. The assassination of Senator Robert Kelly by mutant extremists proved once and for all that humanity was right to fear Homo superior. A chain of tragic events ensued, creating a dark, dystopian future ravaged by nuclear holocaust and ruled by hulking, monolithic Sentinels. Amid this chaos, the last remaining X-Men hatch an outlandish plan to send Kate 'Kitty' Pryde's spirit back in time to inhabit her own teenage body. Once in the past, she must try to prevent Senator Robert Kelly's murder and put an end to their hopeless existence. Collecting Uncanny X-Men #138-143 and Annual #3.