In 1991, the brainwashed super-soldier James “Bucky” Barnes is dispatched from a Hydra base in Siberia to intercept an automobile carrying a case of super-soldier serum. In the present day, approximately one year after Ultron’s defeat in the nation of Sokovia at the hands of the Avengers,[N 1] Steve Rogers, Natasha Romanoff, Sam Wilson, and Wanda Maximoff stop Brock Rumlow from stealing a biological weapon from a lab in Lagos. Rumlow blows himself up, hoping to kill Rogers. When Maximoff throws the explosion into the sky with telekinesis, it damages a nearby building, killing several Wakandan humanitarian workers.
U.S. Secretary of State Thaddeus Ross informs the Avengers that the United Nations (UN) is preparing to pass the Sokovia Accords, which will establish a UN panel to oversee and control the team. The Avengers are divided: Tony Stark supports oversight because of his role in Ultron’s creation and Sokovia’s devastation, while Rogers has more faith in his own judgment than that of a government. At a conference in Vienna where the Accords are to be ratified, a bomb kills King T’Chaka of Wakanda. Security footage indicates the bomber is Barnes, whom T’Chaka’s son, T’Challa, vows to kill. Informed by Sharon Carter of Barnes’ whereabouts and the authorities’ intentions to kill him, Rogers tries to bring in Barnes—his childhood friend and war comrade—himself. Rogers and Wilson track Barnes to Bucharest and attempt to protect him from T’Challa and the authorities, but all four, including T’Challa, are apprehended.
Helmut Zemo tracks down and kills Barnes’ old Hydra handler, stealing a book containing the trigger words that activate Barnes’ brainwashing. Impersonating a psychiatrist sent to interview Barnes, Zemo recites the words to make Barnes obey him. He questions Barnes, then sends him on a rampage to cover his own escape. Rogers stops Barnes and sneaks him away. When Barnes regains his senses, he explains that Zemo is the real Vienna bomber and wanted the location of the Siberian Hydra base, where other brainwashed “Winter Soldiers” are kept in cryogenic stasis. Unwilling to wait for authorization to apprehend Zemo, Rogers and Wilson go rogue, and recruit Maximoff, Clint Barton, and Scott Lang to their cause. With Ross’s permission, Stark assembles a team composed of Romanoff, T’Challa, James Rhodes, Vision, and Peter Parker to capture the renegades. Stark’s team intercepts Rogers’ group at Leipzig/Halle Airport, where they fight until Romanoff allows Rogers and Barnes to escape. The rest of Rogers’ team is captured and detained at the Raft prison, while Rhodes is partially paralyzed after being inadvertently shot down by Vision, and Romanoff goes into exile.