Avengers: Endgame writers Christopher Markus and Stephen McFeely have publicly disagreed with directors Joe and Anthony Russo about how Steve Rogers/Captain America going back in time at the end of the movie to live with Peggy Carter affects the timeline. While the latter have repeatedly said a new timeline would be created by the act, the former have insisted Steve has been in the main continuity all along, though in the background.
One of the main arguments for Steve having created an alternate timeline is that he would be driven to fix some of history's most egregious and devastating events, hence creating a number of different offshoots due to the movie's rules of time travel, However, Markus explained why he doesn't think Steve changed history.
"Stephen [McFeely] and I are just so taken with the idea that Steve went back and somehow, therefore, has always been back," Markus said during a panel Comic-Con International in San Diego 2019, as reported by Screen Rant. "And he got to live his life. Because you get Captain America loyalists who say that if Cap goes back in time, he is honor-bound to fix everything he knows is going to happen. So he has to go save Bucky, he has to prevent the Kennedy assassination... he's a very busy man."
"But that's not why we sent him back," he continued, "We sent him back so that he could become a whole person, and finally come home from the war. We didn't want him to go back and just keep adventuring, we wanted him to rest. And the only way we could come to that solution is if there are two Caps. Which I'm okay with."
Markus and McFeely have previously said Steve Rogers was Peggy's mysterious, unseen husband in Captain America: The Winter Soldier and the father of her children. They also endorsed a popular fan theory that Steve was at Peggy's funeral. Returning as an old man, Rogers passed his shield onto Sam Wilson/Falcon, who will star in an upcoming Disney+ show alongside Bucky Barnes/Winter Soldier.
Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr., Chris Evans, Mark Ruffalo, Chris Hemsworth, Scarlett Johansson, Jeremy Renner, Brie Larson, Paul Rudd, Don Cheadle, Karen Gillan, Danai Gurira and Bradley Cooper, with Josh Brolin as Thanos. The film is now available on Digital HD, Blu-ray and 4K UHD.