The movie is based on the 2006-2007 Marvel Comics Crossover “Civil War”—basically a seven-issue limited series about the Superhero Registration Act, which divided the Marvel Universe into two camps and eventually involved as many as 90 different titles. In the movie, Captain America’s group were Falcon, Bucky Barnes, Ant-Man, Hawkeye, and the Scarlet Witch, and Tony Stark’s group were Black Widow, War Machine, Black Panther, Spiderman, and Vision. But in the comics, the X-Men and the Fantastic Four were broken up as well, and peripheral characters like Luke Cage, The Punisher, She-Hulk, Hercules, Daredevil, Deadpool, Blade, and Ghost-Rider took sides, plus dozens of characters I never heard of. Writer Mark Millar came up with the story idea in 2004, during the George W. Bush administration, when everyone was talking about 9/11, the Patriot Act, and the Iraq Invasion. America thought it was divided. Ah, the good old days. The story was supposed to be an X-Men story, related to the Mutant Registration Act, but it spread. Someone said that Stark sounded like a rich liberal pushing for legislation and Captain America like a staunch libertarian who wanted the government off his back.
The movie opens in 1991, when a brainwashed super-soldier is sent from Hydra in Siberia to intercept a case of super-soldier serum. In the process, he kills a man and a woman. Later, a year after Ultron’s defeat by the Avengers, Steve Rogers/Captain America (Chris Evans), Natasha Romanoff/Black Widow (Scarlet Johansson), Sam Wilson /War Machine (Anthony Mackie), and Wanda Maximoff/Scarlet Witch (Elizabeth Olsen) foil the theft of a biological weapon in Lagos. The would-be thief blows himself up trying to kill Captain America; Scarlet Witch deflects the explosion with her telekinetic powers, accidentally killing some Wakandan humanitarian workers.
U.S. Secretary of State Thaddeus Ross (William Hurt) informs the Avengers that the U.N. is about to pass the Sokovia Accords to control the Avengers and other superheroes. The Avengers’ reaction is varied. Tony Stark/Iron Man (Robert Downey Jr.) supports the idea because he feels guilty about creating Ultron, but Captain America, who knows a thing or two about creeping Fascism, thoroughly disagrees.
Helmut Zemo (Daniel Bruhl) kills a Hydro agent and steals a book containing the words to trigger the brainwashing of Bucky Barnes/Winter Soldier (Sebastian Stan). In Vienna, as the Accords are debated, a bomb kills King T’Chaka of Wakanda (John Kani). The bomber appears to be Barnes. T’Challa (Chadwick Boseman), the king’s son, vows to kill Barnes. Rogers decides to bring in Barnes—his childhood friend--alive. Rogers and Wilson track him to Bucharest, but they are attacked by T’Challa and, after an amazing car-chase in a tunnel, in which we learn what Black Panther is all about, all of them, including T’Challa and James Rhodes (Don Cheadle) are arrested.
Zemo impersonates a psychiatrist and triggers Barnes’ berserker rage. Rogers stops Barnes and hides him. When Barnes comes to, he reveals that Zemo is the bomber and that many other brainwashed Winter Soldiers are kept in cryogenic stasis in Siberia. Everyone’s behaviour changes because of the Accord. Rogers and Wilson, without authorisation, take Scarlet Witch, Hawkeye, and Ant-Man to Siberia to prove Barnes’ innocence. Tony Stark sets out to capture them with Black Widow, T-Challa, Rhodes, Vision (Paul Bettany), and Spiderman (Tom Holland). The big battle at the Leipzig airport is the centrepiece of the movie and one of the most complex and astonishing battles in the Marvel Universe, in which Scarlet Witch, Spider-Man, and particularly Ant-Man are amazing. Some win, some lose, some are injured, and some get away.
Stark learns that Barnes is, in fact, innocent, framed by Zemo to cause friction in the ranks of the Avengers, like Russian internet trolls in an American election. Stark goes rogue himself and strikes a truce with Cap and Barnes, not knowing they have been followed by Black Panther. They find the frozen super-soldiers dead, and then Zemo reveals that the couple Barnes had killed were Stark’s parents. Stark attacks Barnes, Captain America tries to stop him, and we have the second hero versus hero battle of the movie. In the process, Barnes loses his bionic arm, Iron Man’s armour is broken, and Captain America loses his shield. Black Panther gets away with Barnes. In the denouements, Stark provides War Machine with an exoskeleton for his broken legs, Rogers busts the remaining Avengers out of prison, Barnes in Wakanda is put back in cryo-sleep, and Spider-Man studies the new web-shooter Stark built for him.
Tom Holland got the nod for Spider-Man because of his youth and his skills as a dancer and gymnast, but he only received the script one page at a time because he couldn’t resist spilling spoilers. Chadwick Boseman appeared as Black Panther ahead of his origin movie. The Wakandan language was based on Xhosa. The Russo Brothers, who had directed Captain America: The Winter Soldier, directed this one too, and later they would direct Avengers Infinity War and Endgame.