3. At Least Two More Avengers Movies After Age Of Ultron
One of the most important factors in making a Civil War movie - as we've already touched upon in the Agents of S.H.I.E.L.D. entry in this list - is the build-up. This movie absolutely can't be rushed. We need to see the Avengers, as well as S.H.I.E.L.D., gradually drifting apart as far as their opinions on the matter of the Superhuman Registration Act go and that's going to take at least a few more movies. It can't happen in Age of Ultron, because there's still another Avengers movie confirmed - that being Avengers 3, when Thanos will be making his appearance with the Infinity Gauntlet - and the Avengers are absolutely going to have to be a functioning team to go up against Thanos, so there'll be no falling out in that movie, so the rift is going to have to occur in the following movie at the earliest. Whether or not the likes of Robert Downey, Jr. and Chris Evans will even be around by that time (they probably won't, to be fair, but who knows what might happen) is open to debate, but other heroes can take their place (such as the Iron Patriot and the Winter Soldier).
