How the the brilliant finish to a 20+ movie arc was marred by the writing team's wish to give the popular hero a happier ending
Spoilers obviously follow, so if you somehow haven't seen Avengers: Endgame yet and have any intention to, stop reading now.
Avengers: Endgame is an amazing film and is one of my personal favourite movies of all time. The 3-hour epic provided incredible action, one of the smartest approaches to time travel I've seen on the big screen, a surprising number of funny moments, tons of fan service, and managed to bring the Infinity Saga and nearly all of its major character arcs to a satisfying conclusion. For a journey that started over 10 years ago and unfolded over twenty-plus films to be wrapped up so well is no small feat, and the blockbuster wasn't afraid to take risks either.
The death of Scarlett Johansson's Black Widow was an unexpected occurence given the character has a solo film releasing next year, which will obviously be a prequel or origin story given her fate in Endgame. In an even ballsier move, Marvel killed their biggest star in Robert Downey Jr. and brought one of the most compelling character arcs in film history to an emphatic and poetic end. In one final bid of defiance and heroism Tony Stark sealed his fate and fans wept as Iron Man drew his final breaths in a catatonic state; it was a somber and emotional end which wasn't drawn out or overperformed, nor did we see some final grand monologue before his passing (quite surprising for any major film's death scene yet alone in a superhero movie). It was shockingly well done and arguably one of the most impactful and grounded deaths in cinematic history.
With such a loss, the movie had to of course find balance by having some happier endings befall some of our other heroes.
As Iron Man's foil (and yet most trusted ally), Captain America was right there with Iron Man as the second biggest star in the MCU (and Chris Evans sported a massive paycheck to prove it). Yet having featured in so many of the movies and having lost so much in them, it would have been cruel to fans to see him suffer the same fate as Tony in the end as well. So instead, Steve Rogers would get a more uplifting ending.
Now there were several ways they could have done that and the writers actually chose one that worked brilliantly...until it didn't. Instead of leaving the ending more open to interpretation, they had to go and add an extra part which completely broke the time travel rules they had established in the previous two and a half hours.
Note: this is a full-on nerd rant so if you don't want to delve into the details of time travel theory or aren't a Marvel movie fan, then I suggest you find something else to read.
Endgame's Time Travel Rules
Time travel is always a tricky plot device in media given that it is all just a theory, and it tends to get confusing pretty quickly.
Any good film needs to ground their movie in reality - even if the reality in their film is completely different from ours, a film's universe needs to follow a set of rules or fundamental laws even if they differ from those found in real life. If the rules or laws in a movie (or video game, TV show, etc.) aren't clearly established or explained, then anything that diverges from our own reality breaks viewer's immersion into that film.
Viewers can accept insane feats and reality-bending acts if they fit in the established film universe - if something happens that defies the logic outlined in the movie, it is no longer believable to the viewers and thus they are pulled out of the illusion that what happens on the screen fits what they know about the universe explained to them. It's why we can be pulled into the Marvel universe in films - for an overly simplified example, when Doctor Strange magically conjures up a portal that allows people to pass instantly from one location to another, we don't bat an eye, as it's firmly established in the logic of the movies even if we know logically what we're seeing is impossible in our own reality. If however Rocket were to all of a sudden pick a fight with the Hulk and knock him out with a left hook, we would call bullshit right away because it makes no sense in the setting we're viewing it in, despite the fact that both are entirely fictional characters and thus can be made to do whatever a director envisions.
Endgame addresses this aspect early on and as such, establishes pretty clear rules that are explained to viewers naturally and pretty effectively, even poking fun at other famous time travel-themed movies like Back to the Future in the process. So first, let's establish the rules that govern time travel in Endgame.
As explained by Professor Hulk, time travel (at least Marvel's version of it) allows the heroes to travel to the past, then once acquiring what is needed, return to the present, with virtually no time having passed in the present day. Any significant changes made during that travel don't actually affect the past, as that has already happened; instead, they create divergent timelines.
For a simple example, if you travelled 1 year into the past and detonated a nuke that levelled New York City, when you returned to your present day you'd find NYC would still standing and trace of such an event ever occuring - instead, your detonation of a nuke in the past creates an alternate timeline or reality, one in which New York City was levelled, while your own "main" timeline had no such event occur. Thus you are effectively creating an entirely new universe - one in which NYC was destroyed by a nuke - and then returning to your own universe where that never happened and thus you and your reality don't suffer the consequences, but that other universe does.
With this theory of time travel, the heroes don't have to worry about altering their own timeline or future if they change things in the past, however they do have to avoid making significant changes when travelling to the past as they could create potentially horrible outcomes for those alternate realities they created. Basically, even if they successfully save their own reality and future, they could be creating alternate realities which are doomed.
If you're confused, try re-reading the last three paragraphs until it makes sense...or imagine an alternate reality where you understand it. Whichever works for you.
In the film, the heroes venture back to various points in the past (including iconic scenes from previous MCU films) in order to gather the Infinity Stones that were destroyed by Thanos in their future and undo "The Snap" which eliminated 50% of all living beings in the universe. After some trials and tribulations, the heroes accomplish that goal; however, in order to "close the loop" or stop disastrous consequences of their actions from befalling the alternate realities created by removing the Infinity Stones from the past, the heroes have to travel to the past again and put the stones back where and when they were taken. This, in theory, allows those timelines to continue forward uninterrupted and as unchanged as possible in comparison to the "main" timeline.
In essence, they replace the stones where they found them so that alternate realities created through their actions don't suffer from the stones being lost, as replacing them makes it so that they were never lost to those realities at all. Either way, alternate realities exist simply because of the time travel itself, but if all goes well, they'll follow the exact same paths. So far, so good?
Captain America's Ending and Implications
Now if you've seen the movie, you'll recall that near the end Captain America dons his iconic shield one last time and has one last foreshadow-y exchange with his longtime friend Bucky before going to the past and replacing the stones solo. You may have wondered, after how difficult it was to get the stones in the first place even when a full team of Avengers were trying to do so, why on earth Captain America would be sent all by himself to put the stones back and how it could be done so easily...I know I did...but the movie is already 3 hours long, they had to simplify some things somehow.
Difficulty of replacing the stones aside, the crew that saw Cap travel to the past are flabbergasted (aside from Bucky, who knew exactly what his pal Steve did) when the hero doesn't return. And that's where the feel-good ending comes in: after returning the stones to their rightful places, Captain America returned to the 1940s to reunite with his long-lost love, Peggy Carter.
For those that haven't seen Captain America: The First Avenger, Steve Rogers was genetically modified to become a super-soldier in World War II for the US military. After a mission to stop the evil Hydra organization, Steve's aircraft crashes in the arctic and he's encased in ice, though his modified body keeps him alive in effectively a state of cryostasis. He doesn't awaken until some 70+ years have passed and Shield managed to find his frozen body. Thanks to that lost time the world that Steve knew was long gone and all of his acquaintances were either extremely old or dead, including the love of his life, Peggy Carter.
Peggy of course had continued her work for Shield throughout her lifetime, and is a prominent character in the MCU - not only does she feature in Cap's flashbacks in other Captain America and Avengers movies, but she was featured in the Agents of Shield TV show as well as being the star of her own show Agent Carter for several seasons. Of course, her entire life was spent absent the love of her life who was missing and presumed dead all that time; instead she later married someone else and had two children, though the identity of her husband is never revealed.
Later on in the second Captain America movie (The Winter Soldier) Peggy is shown as a 96 year old woman in a retirement home and is reunited with her beloved Steve, who of course hasn't aged a bit thanks to his icy slumber. The scene is especially touching given that for Peggy, she finally got to see her long-lost love after some seventy years apart, yet for Steve, virtually no time has passed and he has to come to terms with the fact that he can never get that time back. Keep that part in mind as it gets important later. She would then pass away off-screen in the third Cap movie, Civil War.
In Endgame, we see Rogers return to the 40s and marry the love of his life, trading in his iconic shield to seemingly live a normal life with Peggy.
It's a satisfying ending and heartwarming to see that the man that sacrificed everything for his country and for the world throughout his life was finally rewarded in the end; of course, the ending creates an alternate timeline that diverges from the main timeline's path but not necessarily one with negative consequences.
In the timeline we've seen unfold over the 20+ MCU films (in what I refer to as the "main" timeline), Captain America is encased in ice for 70+ years and Peggy Carter works as a prolific agent for Shield during that time. We know that she didn't see Steve Rogers again after he was trapped in ice until she was an old woman, as proven by her interaction with Steve in The Winter Soldier. Endgame's ending also implies that the two settled down, and thus it's unlikely Carter continued her work with Shield, at least not to the extensive capacity portrayed in the Marvel shows, and she obviously didn't marry another man and have two children with him while she was married to Steve.
This alternate reality would also have two Steve Rogers - the one still encased in ice in the Arctic that will only wake up in the 2000s, and the Cap we know and love from Endgame and the other Marvel movies, who helped save the world from Thanos then returned to the past and stayed there. This reality would have Peggy Carter either retiring from Shield or at the very least taking a much less extensive role with the company and their deeds, and other potential changes given future Steve's presence there; how much that affects that reality would be unknown, but it's a different timeline nonetheless.
Instead of leaving it at that and letting fans wonder, which would have worked just fine and presented no real "plot holes" as it would just be an alternate timeline we haven't explored, the writers chose to have a heavily aged Steve Rogers show up to pass on his Captain America mantle.
In this contentious scene, an old and wrinkly Steve is seen sitting on a park bench near where he travelled to the past just moments earlier (at least it was only moments for everyone else in the present day) and is approached by a bewildered Sam (Falcon), who clues in that he is in fact looking at a much older version of his friend Steve. Cap passes on his iconic shield and tells him that he lived a great life and finally made a decision to live the life he spent so long wishing for. Of course, many fans were also confused by the fact that Steve was passing on the Captain America shield and title to Sam rather than Bucky, who was a more logical fit. Bucky of course was his longtime best bud and also took over as Cap before passing it down to Sam in the comics, where Marvel has opted to skip over Bucky in their cinematic universe (another diverging timeline perhaps? *wink wink*).
Regardless of who he chose to give his shield to, the scene was a major error for an entirely different reason - it appeared to completely contradict the time travel rules already established in the movie.
Changing the past does not change the future; it creates a new future, an alternate timeline, as clearly established in the movie. When Steve stays in the past and marries Peggy, this completely changes what happens in their future and diverges from the main timeline - if it was a closed loop as the scene suggests simply by Steve's presence, then the 96-year old Peggy who hadn't seen Steve since 1945 couldn't exist, as she would have been with Steve the entire time. Fans have also pointed out the fact that the Steve sitting on the bench would have had to have been well over 100 by then since the Steve that travelled to the past was at least in his 30's at the time, but that aspect can easily be explained thanks to the super-soldier serum that gave Captain America his abilities; it not only made him immune to most diseases and illnesses, but its regenerative properties slowed the aging process significantly.
Him sitting there in the main timeline here simply makes no sense in the context of the movie and the entire MCU.
If it's a closed loop as the scene suggests, then all of the prior events shown in the MCU of Peggy Carter after Steve was trapped in ice never happened, including her marrying and having children with another man and all of the events that happened in Agent Carter. Her old-age reunion with young Steve in the retirement home in The Winter Soldier also then makes no sense as she would have never been without him. It would essentially be saying tons of events we've seen happen in the MCU never happened or were fake, and simply doesn't work.
The Russo Brothers' Answer
Since the online communities have been trying to wrap their head around this confusing plot hole, the Russo brothers (directors of Avengers: Endgame and Infinity War before it) came out and presented how it happened.
In their rather solid explanation, Steve going back to the 1940s to live his life with Peggy Carter created a branch (alternate) reality, in the same way as explained above. To get back in the "main" timeline however, an old Steve who stayed in that timeline until the present day, used remaining Pym Particles that he had saved to travel "back" to the modern day and hand off his shield.
This is supported in multiple ways by scenes in the film. For instance, when Cap goes back to the 40s with Tony to grab extra Pym Particles needed for their mission, he sees Peggy in the military base which is where he obviously gets the idea to return to that time period. He also takes more Pym Particles than what's required, which is highlighted by the fact the camera lingers on this fact after he takes the vials - clearly the Russos are foreshadowing Cap's plan which requires more Pym Particles than Tony's plan.
The quantum suits created by Tony Stark and used by the Avengers in the film use Pym Particles to travel to the past, and the large platform seen in the film is only required when one wants to get back to the present day (thus travelling forward in time rather than back).
So the Russos explanation is that Cap returned the stones to their places, then travelled back to the 1940s as we saw in the movie. He stayed in that divergent timeline until the present day (in 2023) passed, then used the extra Pym Particles he had saved to travel back to the present day. Since travelling backward in time doesn't require use of the platform and you can pick a precise location as figured out by Tony and Steve in the movie, he would then not have needed to appear on the platform and could easily have just chosen to travel to the park bench where he met Sam and Bucky in the film.
While that explanation makes sense in many ways and effectively explains the ending doesn't actually defy their rules, it still raises more questions and some serious moral implications.
First off, what happened in this alternate timeline? This alternate universe would have had two Steve Rogers - the one that awoke from the ice in the 2000s and went on to lead The Avengers and fight Thanos, and the one who travelled back in time and married Peggy. Did young Cap ever discover this in this timeline? How did Peggy not being in Shield affect the world? A man of his fame would have had to have stayed hidden or in disguise to not be dragged bag into his old life, which given his training and that Peggy is a spy wouldn't have been unrealistic, but to keep himself hidden for that long and not use his knowledge and ability to influence future events? Would a man as moral as Steve Rogers simply sit idly by while he knew Hydra was in Shield's ranks and thus simply allow many innocent people to die when a simple phone call could stop it?
And then there are the many questions regarding Peggy Carter and the MCU's writers regular hints since Endgame's release that Mr. Carter, who Peggy married and had two children with long after Cap went missing, was none other than Steve Rogers himself. If that's the case, then even with the Russos' explanation their time travel rules were broken, as despite an alternate reality being created we have a loop where changing the past effected the future. If that's true, are we to believe that Captain America hid in the background for decades and stayed mute even when he knew vital information regarding future events that could have saved lives? And he simply hid when young Steve met with old Peggy in the retirement home, where she lied about her husband's identity in order to not affect future events?
The writers even seemed to confirm one theory over social media: that a grey-haired pallbearer helping carry Peggy's coffin behind Steve at Peggy Carter's funeral in Civil War, whose face we never see in the movie, is actually an old Steve Rogers, or "Mr. Carter". If that's the case, then how would young Steve not recognize an older version of himself? Would the Steve we know from all the Marvel movies really wear a disguise to attend the love of his life's funeral? And that would confirm he stood by and let events unfold as they happened even when he knew about Hydra's infiltration of Shield and other events in which many people died, something th