Secret identities don't matter. It was really about holding superheroes accountable to protect the world. That's what we'll see in Captain America: Civil War according to Joe Russo who spoke with Empire to help answer questions about the film's first trailer.
"We're using the essence of what Civil War was about. The comic book isn’t applicable to the storytelling that we’ve structured up to this point, but the concept of registration, the notion that heroes need to be either monitored or controlled because their power can be scary, is applicable."
First mentioned in the post-credits button of Ant-Man which featured scenes of Sam Wilson a.k.a. Falcon (Anthony Mackie) and Steve Rogers a.k.a. Captain America (Chris Evans) speaking with Bucky Barnes a.k.a. The Winter Soldier (Sebastian Stan) are "the accords" which we now to be the Sokovia Accords - the MCU's equivalent legislation to the Superhero Registration Act.
"The Accords are the world jointly trying to govern the Avengers moving forward. It has to do with the effects of Ultron and Sokovia [the small city that Ultron tried to drop on the Earth from a great height at the end of Age Of Ultron], and New York City [roundly trashed at the end of The Avengers], and Washington D.C. [nearly devastated by falling helicarriers at the end of Captain America: The Winter Soldier]. Examining the third acts of all the Marvel movies, we’re saying, if you could point to the collateral damage in all those incidents, could you use that against the Avengers to control them?"
Interestingly, in the comics, the Civil War debacle was set squarely in the U.S. after a U.S. incident but the movie version makes it appropriately broader and international. It's based on the events of Avengers: Age of Ultron which saw a nation in Eastern Europe devastated by a creation of the Avengers, and another international incident teased in the Captain America: Civil War synopsis that's yet to be revealed.
Better yet, the film version will explore the grey area of the conflict itself with the goal of making audiences split down the middle in who they side with. It won't be like the books where Tony Stark is basically a villain. Both Stark and Rogers will have appropriately strong motivations for their actions in the film.
The political nature of Captain America: Civil War and its themes fittingly draw comparisons to Batman V Superman: Dawn of Justice which similarly pits two iconic heroes against one another after the events of Man of Steel which saw horrifying collateral damage in Metropolis as a result of Superman battling his brethren, alien forces attempting to convert the planet into their new home.
In both films, there's a third antagonistic party waiting in the wings. For BvS, that villain who unites the heroes is rumored to be the monstrous Doomsday where in Captain America 3 we know Daniel Bruhl to be playing a version of classic Hydra villain Baron Zemo.
The movie stars Chris Evans, Robert Downey Jr., Scarlett Johansson, Sebastian Stan, Anthony Mackie, Emily VanCamp, Don Cheadle, Jeremy Renner, Chadwick Boseman, Paul Bettany, Elizabeth Olsen, Paul Rudd, Frank Grillo, Tom Holland, with William Hurt and Daniel Brühl. Marvel’s “Captain America: Civil War” is directed by Anthony & Joe Russo and produced by Kevin Feige. Louis D’Esposito, Alan Fine, Victoria Alonso, Patricia Whitcher, Nate Moore and Stan Lee serve as executive producers and the screenplay is by Christopher Markus & Stephen McFeely.
Captain America: Civil War will release on May 6, 2016, followed by Doctor Strange - November 4, 2016; Guardians of the Galaxy 2 - May 5, 2017; Spider-Man - July 28, 2017; Thor: Ragnarok - November 3, 2017; Black Panther - February 16, 2018; The Avengers: Infinity War Part 1 - May 4, 2018; Ant-Man and the Wasp - July 6, 2018; Captain Marvel - March 8, 2019; The Avengers: Infinity War Part 2 – May 3, 2019; Inhumans – July 12, 2019; and as-yet untitled Marvel movies on May 1, July 10 and November 6, 2020.