In a movie full of satisfying conclusions, Captain America got arguably the best ending in Avengers: Endgame. After defeating Thanos, the "first Avenger" traveled back in time to return the Infinity Stones and decided to stay there, spending the rest of his life with his one true love, Peggy Carter.
But what if Captain America didn't just disappear into the past but actually had a major influence on the course of history in the Marvel Cinematic Universe after leaving the Avengers in Endgame? An intriguing new theory about Peggy's experience as the Director of S.H.I.E.L.D. in the 1970s could reveal another key way this scrawny boy from Brooklyn changed the MCU for the better.
Writing in the Fan Theories subreddit, redditor u/spacelincoln argued that Peggy Carter her own "Sokovia Accords moment" similar to Cap' in Civil War. What does that mean? Well, we know Peggy was director of SHIELD in 1970 and we also know she eventually left the organization. We also know the group originally existed within the U.S. military but fell under the jurisdiction of the World Security Council by the time the Avengers were formed.
So what happened? It makes sense that, similar to the Avengers in Civil War, as SHIELD's influence and power grew the United Nations attempted to take control of the organization. In response, Peggy may have quit her job out of protest. At least, that's what this theory suggests.
But what's really interesting here is the parallels the theory draws between Captain America's decisions in Civil War and Peggy's alleged choice decades earlier. So why would she refuse to accept this new bureaucratic oversight?
Here's my theory: Captain America pushed Peggy Carter to quit SHIELD. This fits perfectly with his character and helps explain a minor mystery in the Marvel Cinematic Universe.
The only issue here is that, according to Bruce Banner/Hulk in Avengers: Endgame, you can't change the past via time travel. According to the movie's logic, traveling back in time creates a new branch of reality unrelated to the main one you originally came from. If that's the case, Captain America couldn't alter the MCU through time travel, though it's worth noting that Endgame barely sticks to its own rules in this regard. (How did old man Cap even get back to this reality to pass the torch to Falcon if he's in a different branch of reality?)
The truth is that once you start thinking too much about time travel in Avengers: Endgame it all falls apart, which kind of gives us free rein to come up with any theories we want. And in that case, why not indulge in a theory that helps fill in the blanks on Cap' and Peggy's happily-ever-after ending?