The introduction of Spider-Man in Captain America: Civil War (and into the Marvel Cinematic Universe proper) was a major beat of the movie. While Spidey doesn't hang around for the entire film, his two sequences help to guide the plot and reveal a lot that's going on within the larger world of the MCU. That said, it almost didn't happen.
The writers of Civil War have mentioned before that there was a time when they weren't sure if Spider-Man would make it into the film. Now, they've gone into more detail on why and revealed that they could have replaced him in the script much more easily than fans might think.
During a recent interview with Creative Screenwriter Magazine, Captain America: Civil War screenwriters Stephen McFeely and Christopher Markus opened about what went into adding Spider-Man to the movie. According to McFeely, Spider-Man was "in and out all over the place" because they weren't quite sure if they'd be able to use him. They knew that if they could use him, they wanted him to be part of the "splash panel" scene that McFeely described as such:
"From the very beginning, we knew if we called something Civil War we were going to have to pay off what we called the 'splash panel,' which is that seventeen-minute fight where everyone goes at it. It was incumbent upon us to try to fill that with as many heroes as we could without breaking it or forcing people in. We always had a little recruitment section where Tony would get somebody and Steve would get somebody and the rosters would fill organically."
He went on to explain that Spider-Man was "always our first choice for that" due to Kevin Feige telling the duo that there was a chance Spider-Man could be available. Feige explained that conversations were going on with Sony, so McFeely and Markus added him in tentatively. There were times that it didn't seem like such a sure thing, however, as McFeely explained:
"We had him in, and sometimes a month or two later Kevin would come back and say, 'No, negotiations are not going quite as well. Don’t plan on him!' [Laughs] I don’t know the exact date when corporate signed contracts with Sony, but it eventually led to some hard and fast choices later on."
The uncertainty about Spider-Man's availability wasn't necessarily difficult to work around, however. After all, his main appearance was slated to be in that "splash panel" scene. That made him replaceable if necessary, as Markus explained:
"In that regard, it was very good that he was in a section where the script would’ve called for somebody there, but there wasn’t necessarily a tremendous amount of quantum mechanics riding on that it had to be Spider-Man. So if we finally didn’t get him, the whole house of cards wouldn’t fall down. It would just mean we would have to come up with a different character to play that function."
Ultimately, of course, things worked out and Spider-Man was used to great effect in the big battle between Team Cap and Team Iron Man. It's hard to imagine how things might have gone if a different hero had been selected, or what character could might have fit into the narrative as easily as Spider-Man did. Given how many Marvel heroes are being hidden away in the MCU's various movies and TV shows, though, Markus and McFeely certainly would have come up with someone.
Captain America: Civil War is in theaters now. Doctor Strange opens November 4, 2016; Guardians of the Galaxy Vol. 2 – May 5, 2017; Spider-Man: Homecoming – July 7, 2017; Thor: Ragnarok – November 3, 2017; Black Panther– February 16, 2018; Avengers: Infinity War Part 1 – May 4, 2018; Ant-Man and the Wasp – July 6, 2018; Captain Marvel– March 8, 2019; Avengers: Infinity War Part 2– May 3, 2019; and as-yet untitled Marvel movies on July 12, 2019, and on May 1, July 10, and November 6 in 2020.