Just like the original 2006 storyline, Captain America: Civil War’s main draw is the conflict between the heroes over new legislation that will regulate and police their actions. The new status quo change will see the Avengers fractured and facing off against each other, most notably the Star Spangled Avenger himself and Iron Man. This is a story that’s painted in shades of grey rather than black and white, so no one is truly "right or wrong" when it comes to this issue. However, given that this is a Captain America movie, Tony Stark comes out looking more antagonistic, and Robert Downey Jr is okay with that.
While Iron Man isn’t the clear-cut "bad guy" in the movie (that belongs to the likes of Crossbones and Zemo), Downey explained to EW that Tony is comfortable with being the main antagonist given that his character’s habit of making things worse gives him a different perspective. Downey said:
I’ve always thought of it in some ways that Tony is the antagonist to himself in his own story, so this isn’t a problem. This guy understands problems ‘cause he is a problem. And he tends to create problems. I’m not having to patter around what I think the worldview is. I wholeheartedly agree with what he does in this. Which is, by the way, more than I could say for some of the other movies.
Creating problems is an understatement when it comes to Tony’s history in the MCU. Even ignoring his past building and selling weapons without considering the consequences, his actions as a superhero have inadvertently led to threats emerging, whether it was humiliating Aldrich Killian and leading the man to create AIM or Ultron becoming sentient and trying to wipe out all life on Earth. After years of seeing what unrestricted power is capable of, Tony now believes that limitations are needed to separate the heroes from the bad guys, an opinion that the movie’s main hero Steve Rogers doesn’t share, which will drive a wedge in their friendship.
Following Sokovia’s destruction in Avengers: Age of Ultron and another still-unseen "international incident" that results in collateral damage, Captain America: Civil War will see the world’s governments drafting the Sokovia Accords, legislation that will make it so that Earth’s Mightiest Heroes can’t operate without express consent from a panel formed by the United Nations. Iron Man will be one of the lead proponents for registering, and along with War Machine, Black Widow, Black Panther and Vision, he’ll hunt down anti-registration advocate Captain America, who is allied with Winter Soldier, Hawkeye, Scarlet Witch and Ant-Man.
Captain America: Civil War will be released on May 6, 2016.
