Hints of the war between superheroes were sprinkled in "Avengers: Age of Ultron" and "Ant-Man" and all will come to a clash in next year's "Captain America: Civil War." According to a report from Heroic Hollywood, the incident that will trigger the war will be caused by Captain America (Chris Evans) trying to apprehend Crossbones (Frank Grillo). 

The official synopsis of the movie states that an international incident that involves the Avengers causes massive collateral damage which forces government control over the team and other super-powered beings. This control or policy was referrenced in the post-credits scene in "Ant-Man" as the "Sokovia Accords." 

The "Sokovia Accords" directly refer to the city of Sokovia which was levitated and then dropped during the events in "Avengers: Age of Ultron," an event which destroyed the city and presumably killed hundreds of people in the process. 

Heroic Hollywood claims that the incident being described in the synopsis involves Captain America and Scarlet Witch (Elizabeth Olsen) trying to catch Crossbones. However, Crossbones is equipped with a vest full of explosives, which forces Captain America to ask Scarlet Witch to levitate Crossbones out of the vicinity. 

This fails and the explosives set off, instantly destroying the building while also harming numerous civilians in the process. This will be the incident that forces the government to order when an Avenger is to be sent, how their training will be conducted, and how far S.H.I.E.L.D. can go in order to control super-powered beings. 

In the comic books, it is the U.S. government that forces regulation on the superheroes but in the cinematic universe, it is being implied that this is now an international concern. 

In the comic books, Iron Man (Robert Downey Jr.) decides to side with the government while Captain America does not. It makes sense for Iron Man to sign up for the Accords given how Ultron was his creation. 

However, as pointed out in a report from Cinema Blend, these are still unconfirmed rumors so they must be taken with a grain of salt.

"Captain America: Civil War" is currently in production and more details are expected to emerge as it nears its May 6, 2016 release date.