One big twist in the movie, Captain America: Civil War had been about the history of the Marvel Cinematic Universe. It was revealed that Steve Rogers’ friend, Bucky Barnes, had been the one who killed Tony Stark’s parents. He had been controlled during that time and was not aware of his actions, but he is still the one who is physically responsible. Captain America had kept this a huge secret from Tony and wanted to protect him, and this bit him later on. Today is the death anniversary of Tony’s parents, aka, Mission Report Day.
All throughout this movie, Zemo had tried to get information about this mission from Bucky and wanted to bring down the Avengers. He then asks him many times occasions for “Mission report: December 16, 1991,” and wanted to get the details about the death of the Starks.
It then took Zemo many attempts to get through and then Bucky is imprisoned, and he poses as an employee of the United Nations to read all of his activation words. In Russian, Zemo then reads the following code:
Steve then backs Bucky as Tony learns about the truth. They then fight almost to death. They then do not speak for years, and the next time they meet, Thanos had decimated half of the known universe.