Under the command of Magneto, a worldwide army of mutants attacked humanity relentlessly. During this Mutant War, every super-powered being on the planet was pitted against Magneto's mutant soldiers. Acts of terrorism on American soil were commonplace, and many heroes were killed.
Unbeknownst to the rest of the world, Tony Stark was actually funding Magneto's terror operations to both thin out the meta-human population and ultimately become leader of the remaining bits of humanity.
Stark got his wish, only on his own terms. He murdered Magneto in battle on worldwide television, making Iron Man the Hero of the Mutant War.