A mutant-generated explosion that destroys most of Stamford, Connecticut, leads to the Superhero Registration Act, which requires superheroes to unmask publicly and register with the government. The law causes a division in the ranks of the superheroes, and, alligned behind Iron Man Tony Stark, who becomes an enforcer for the new law, and Captain America Steve Rogers, who sees the law as violating civil liberty, the superhero community begins a civil war.