The full story
The Sokovia Accords change everything. After the devastating events in Sokovia and a botched mission in Lagos that kills Wakandan aid workers, the world demands accountability. The United Nations proposes oversight of the Avengers, and the team fractures along fault lines that have been building since the beginning.
Tony Stark, haunted by Ultron and confronted by a grieving mother whose son died in Sokovia, supports the Accords. He sees regulation as the responsible path forward. Steve Rogers refuses to sign. He has witnessed government institutions corrupted from within by HYDRA and will not surrender the Avengers' autonomy to a committee with agendas.
Then Bucky Barnes re-enters the picture. A bombing at the UN kills King T'Chaka of Wakanda, and footage points to the Winter Soldier. Steve knows his friend was brainwashed by HYDRA for decades and believes Bucky is being framed. He's right—the real bomber is Helmut Zemo, a Sokovian whose family died when Ultron dropped a city from the sky.
Zemo isn't interested in world domination. He wants to destroy the Avengers from within, and his plan is devastatingly simple: expose the truth about December 16, 1991. On that night, the Winter Soldier assassinated Howard and Maria Stark. Bucky killed Tony's parents.
The airport battle in Leipzig features Team Cap versus Team Iron Man, with the debut of Spider-Man (recruited by Tony) and Giant-Man (Scott Lang transforming to enormous size for the first time). Rhodey takes a devastating fall that leaves him partially paralyzed. Steve and Bucky escape while Sam, Clint, Wanda, and Scott are imprisoned in the Raft.
But the real climax happens in Siberia. Tony learns the truth about his parents in the worst possible way—watching the footage with Bucky standing right there. The fight that follows isn't about ideology anymore. It's raw grief and rage. Steve chooses Bucky, and Tony is left alone in a frozen bunker, the Avengers shattered.
T'Challa, whose father died in the bombing, spends the film hunting Bucky for vengeance. When he witnesses what revenge has done to Zemo and recognizes what it nearly did to himself, he chooses a different path. He offers Bucky sanctuary in Wakanda, completing his transformation from a man driven by vengeance to one who chooses mercy.
Civil War leaves the Avengers broken. Steve Rogers is a fugitive. Tony Stark is isolated. The team that once stood together is now divided.