Captain America: Civil War - 16 Things We Learned From The Directors' Commentary
15. The Writers Came Before The Film Idea
As an indication of Kevin Feige's faith in the Russos and the writing team after the excellent The Winter Soldier, all four were invited back for the sequel. According to the commentary, that came even before the final idea for the film was even decided.
Feige asked the creative team if they were interested even before discussions were underway, and despite the fact that the MCU was already headed towards friction between Cap and Iron Man, Civil War was only one possible option.
The team actually spent months going through possible story ideas before finally coming to that decision, realising that there was a lot of potential to build on Tony Stark's guilt coming out of Age Of Ultron.