“[…] it will be Crossbones (in costume) who will be the catalyst that kicks off the film, instigating an attack that causes much death and destruction, causing the government to step in and put out the Superhero Registration Act.
The other element that will be a key focus is The Winter Soldier, whose existence is the big question as he has the ability to be a hero, but has also been a villain. This causes the main rift between Tony Stark and Steve Rogers, as the disagreement leads them to opposing sides.”
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JoBlo on the Captain America: Civil War story.