“Civil War” is a giant multiseries “event” thing from a decade ago, containing the deaths of major characters, and pitting half of the Marvel-universe heroes against the other half. If I were them, I would not be trying to pull off this story when the Avengers (as a group) are still in their early going as a film franchise. But they say that the development process for the Marvel Cinematic Universe is full of contingency plans, including plans for when key actors are no longer available... maybe they’re doing this now because somebody wants out. I’ve heard rumors of certain persons being tired of having to constantly bodybuild.
Be that as it may, the sides chosen in this civil war seem out of character for how the personalities involved have been set up in the prior films. I am feeling pretty dubious about this one. It might be in this film that the wheels start to come off the Avengers train.