In Captain America: Civil War, a dispute over the Sokovia Accords and the fate of Bucky Barnes led to a schism in the Avengers’ ranks, with Earth’s Mightiest Heroes forced to choose sides between Iron Man and Captain America. However, Tony Stark and his newfound ally T'Challa/Black Panther almost didn't make it into the film.
"So while Joe and Anthony Russo and Chris [Evans] and Marcus and Steve McFeeley and Nate Moore on [Civil War] were in the room developing, I'd be running in and out being like, 'I think it's gonna be Spidey!'" Feige recalled while speaking at the New York Film Academy. "And then I'd go, 'Forget it! Not gonna work!' And also, by the way, even Downey -- we didn't have a deal with Downey, so it's like, 'Looking good on Downey!' 'Okay, it's Cap vs. Iron Man.' 'I don't know, it might not be Downey.' 'Alright, so it's going to be Cap vs. who?' So we started developing, not writing full versions, but being prepared to make a shift if we had to, because like I said before, we choose a movie, we announce a movie, it's coming out."
https://m.youtube.com/watch?time_continue=1&feature=emb_title&v=d_P8V6KPnoc
"We've been very lucky that usually it's worked out," he continued. "It was during those conversations that Nate said, 'What about Black Panther? What about bringing T'Challa into this Civil War as a third party who didn't have an allegiance to either side, who had his own issue, and -- if we don't have Spider-Man and God forbid if we didn't get Robert -- there'd be another element, a new, fresh element to make the movie worthwhile?' We ended up getting it all and it ended up being great, but it can vary."
Next up in the Marvel Cinematic Universe is Black Widow. Directed by Cate Shortland, the film stars Scarlett Johansson as Natasha aka Black Widow, Florence Pugh stars as Yelena, David Harbour as Alexei aka The Red Guardian and Rachel Weisz as Melina. The film opens May 1, 2020.