The movie started in 1991 where Hydra being brought from a cryogenic chamber, his captors had a book that contains instructions on how to make him obedient to their command. He was then dispatched to steal a briefcase and leave no witnesses. This is later tied to the main storyline of the movie - similar to the Iron Man 3 where the something that happened in the past comes back to haunt us. As for the what led to the civil war, the destructions and bystanders killed in the earlier movies - Avengers, Captain America 2, Avengers 2 placed pressure on the government to control the Avengers. However, Peggy Carter reminded Captain America that sometimes it is necessary to stand up for what is right even if everybody else disagrees. The Sokovia Accord was proposed to place the Avengers under the jurisdiction of the United Nations. Tony Stark immediately supported the proposal because of of the guilt he felt after he was confronted by one of the mothers of victims in Sokovia. Steve on the...