Now before you get mad at me for this theory, I'm not saying that he instigated the fight that took place in Captain America: Civil War, but he did help cause it to happen. Heck, if he hadn't been around at all, it would have probably happened sooner! Think about it...
Nick Fury, as director of S.H.I.E.L.D., was responsible for bring together the world's mightiest heroes. With all of the different personalities that were involved, they started to butt heads. In the fist Avengers movie, there was a scene where they were all arguing on the first day they were together as a group, right before Hawkeye's attack team showed up. That situation was diffused when the team was forced to defend their Helocarrier. After Coulson "died," Fury manipulated the facts in order to bring the team together for the fight against Loki, which worked. In Captain America: The Winter Soldier, he was the only one that Rogers would really listen to, even when they disagreed on what should or shouldn't be done. The two came up with a plan, and they saved the world from HYDRA. In Avengers: Age of Ultron, when the team was down and out and hiding at Haweye's farm house, who galvanized the team and brought them back together? Nick Fury. He even helped save all of the civilians by bringing a Helocarrier out of mothball and flying it up to load everyone onto it. He wasn't even a part of S.H.I.E.L.D. at that time, but he knew how to bring the team together. He has been able to help bring the Avengers together each time they were on the verge of collapse.
Then we get to Captain America: Civil War. Guess who was noticeably missing from that film? Nick Fury! And what happens in that film? They all go bat-crap crazy and start warring against each other! The Russo brothers have even said that the fallout from that movie will spill into Avengers: Infinity War, so who do you think they'll get to diffuse all of the tension that is sure to be there? Hopefully, Nick Fury. When asked if he was going to be in the next Avengers movie, Samuel L. Jackson had this to say on the matter:
“Yeah! For sure, definitely. Why wouldn’t there be? There’s some way of fixing what they created, and hopefully somebody has that going on or Nick Fury is out there — wherever he is, probably hanging out with Jules and walking the world — figuring out what happened and how it got to that particular place. Maybe they’ll find out that all that was part of a ruse to get to something else also. That would be great. They’ll bring me back somehow, some way, for some reason. I mean, they didn’t have me around to referee the kids when they didn’t go to their rooms and got in this big old fight. We’ll see what happens.”
His absences has caused a ripple affect throughout the entire MCU, and the only way that it might be saved is by having Nick Fury come in and clean up the mess that our heroes have caused. Of course, this is just my opinion, and you are more than welcome to disagree with me, but if you do, make sure you have an argument to back you up against this theory. Let me know what you think in the comments section down below.