Avengers: Infinity War has been out for a month and change, and is certainly one of the most ambitious and expensive movies of all time. While Marvel fans were eager to see the shared universe's heroes and villains unite against Thanos, it wasn't long ago that Captain America: Civil War was the biggest crossover movie. That film was basically a test run for The Russo Brothers' ability to juggle a ton of characters, as most of the MCU's heroes faced off against each other in an epic tarmac battle. While the lines were drawn in Civil War, it turns out that Paul Rudd's Ant-Man wasn't always going to be on Team Cap. As writers Chris Markus and Stephen McFeely recently revealed, Scott Lang was going to be on Iron Man's team if Sony didn't give Marvel the rights to include Spider-Man. As they told it,
McFeely: [Tony Stark] would recruit somebody else. He probably recruits Ant-Man, I think would be that idea. Well, we had a section where you could recruit somebody, right?
Markus: [Tony] actually went to San Francisco. It would not have been as cool.
McFeely: I believe [Scott] was watching his daughter play soccer. It wasn't very good.
While the writers of Civil War and Infinity War may have had a back up plan in mind, it looks like they were really hoping Spider-Man would be introduced in the MCU. Luckily it happened, and Tom Holland's Peter Parker became an instant fan favorite, despite having a relatively small role in the Captain America threequel.
Stephen McFeely and Chris Markus' comments about Civil War come from their recent appearance on Kevin Smith's podcast Fatman on Batman. The duo have been very involved in the Marvel Cinematic Universe over the years, writing all three Captain America movies and Thor: The Dark World before eventually working on Phase Three's Avengers movies.
The duo of writers certainly had their job cut out for them with Civil War. In addition to crafting a story for its title character, they also had to work with the other members of The Avengers, as well as introduce two new heroes. Spider-Man and Black Panther both made their debut in the threequel, ultimately taking Tony Stark's side in the titular conflict. This allowed for Paul Rudd's Ant-Man to join Team Cap, which is arguably more his style. The guy is a professional criminal; he doesn't seem like the type to enforce The Sokovia Accords.