Ultimate X-Men Volume 5: Ultimate War

When the X-Men do the worst thing they could do to humanity, the government orders Captain America, Iron Man, Thor, and the rest of the Ultimates to bring them down. A small but lethal army, the Ultimates were created to face these and other newly rising threats to mankind. But the X-Men's founder, Professor X, hasn't been training his students for nothing - and the young mutants just might take out the Ultimates first.

Collecting Ultimate War #1-4.