It's clear that the Marvel Cinematic Universe is setting up two opposing sides in superherodom already, with Tony Stark managing to p*ss off most of his Avengers colleagues with his reckless actions in Age Of Ultron. That's giving a bit of a lead-in to Civil War, just as the comics were a culmination of a bunch of plotlines. But it was one inciting incident really kicked the source material off. Namely, an untested and untrained team of young heroes called the New Warriors whose exploits are filmed for a reality show, kids these days eh attack a supervillain safe house and it goes a bit wrong. Which is to say one of the villains, called Nitro, detonates himself and causes a huge explosion in a small suburb. And he does that whilst a school bus is driving past, meaning loads of kids die. Civil War, in the comics, begins because some superheroes accidentally let a bad guy murder lots of small children. That's a little bit too hardcore for the movies. Obviously the third Captain America will have no New Warriors, but hopefully it won't be as violent either, because it'd be tonally off-base. And gross.