In the aftermath of the Ultron disaster, Captain America and the rest of the Avengers come under closer scrutiny by world governments concerned by the collateral damage that occurs whenever the Avengers act. Some of that concern stems from lack of control and oversight of "enhanced humans". The United Nations puts forth the Sokovia Accords which effectively places the Avengers under U.N. control. This leads to a schism within the Avengers: Iron Man leads those who would sign the accords and Captain America lead the faction that doesn't trust the U.N. to call the shots.
Captain America's friend Bucky (The Winter Soldier) is implicated in carrying out a bombing mission at the Vienna meeting to ratify the accords. Many die in the attack, including the king of the African nation of Wakanda, King T'Chaka.
The Avengers reach their first crisis. Will they stand by and watch the U.N. carry out orders to kill Bucky, or will they follow Captain America's plan to capture Bucky to see that he gets due process?
Captain America locates Bucky and attempts his rescue, but eventually Cap is arrested by government forces. along with Bucky, Falcon, and T'Challa (Black Panther - who is seeking to kill Bucky as revenge for the death of his father in the explosion at the signing ceremony). But the detention facility is infiltrated by Sokovian Colonel Helmut Zemo, posing as a government interrogator. Zemo, using code word triggers, activates Bucky's Winter Soldier brainwashing, gets vital information from him, and then sends him our to wreak havoc as Zemo escapes.
Civil War breaks out among the Avengers. Iron Man and his team are tasked with arresting Captain America and his rebel Avengers. Captain America wants to save his friend, Bucky, and stop Col. Zemo from carrying out a catastrophic plan. Ultimately, they must discover if whether the goals that brought the Avengers together are stronger than the forces arrayed to drive them apart.
Movie Sermon's General Warning
Captain America: Civil War contains some vulgar language and a tremendous amount of battle violence.