Following a Super Hero operation that resulted in many casualties, the Superhuman Registration Act was ratified, forcing heroes to reveal their secret identities and subject themselves to government oversight. Iron Man agreed with the policy and put together a team of Pro-Registration heroes around him to enforce it. Captain America, on the other hand, felt heroes had to be above direct government control. Soon other Anti-Registration heroes joined him, becoming outlaws and forming the Secret Avengers. Inevitably a violent conflict broke out between the two sides and now the villains sit by the sidelines as once-allied heroes fight against each other in an all-out Civil War!

This expansion introduces an entirely new way of playing Marvel United! The Civil War play modes make it a true Player vs Player game, in which two teams of Heroes battle against each other, with no Villain in sight. Featuring a roster of Heroes from both sides of the Registration conflict, this expansion adds two ways for players to fight each other: either the more casual Clash of Heroes, or the more competitive, asymmetrical, and thematic Registration Clash! Which team will you choose?