Following the events of Avengers: Age of Ultron, the government believes superheroes are in need of supervision. Iron Man is in full agreement, but Cap wants no part of it. This may be in part because the government happens to be out to kill Cap's old friend Bucky (Sebastian Stan).
This rift between Iron Man and Captain divides the Avengers straight down the middle. Plus, there will be a few new faces joining the fight. Civil War will also include the first appearance of Black Panther (Chadwick Boseman), whom you can see a few brief glimpses of in the trailer.
Captain America: Civil War hits theaters May 6.