(Warning: The following contains giant, hulking plot SPOILERS for Captain America: Civil War, particularly in the area of character motivation. If you haven't yet seen the movie, then proceed with whatever level of caution that suggests to you is wise...)
Now, while the past few months of endless, torturous, impatient waiting for Captain America: Civil War to hit theaters were certainly tough, there was - in the cold light of it finally having arrived - at least one upside to the experience: We got to spend months speculating about just what we'd see happen in the final movie. One particularly popular source of debate? Why the film's leading superheroes would choose the side they're on in the movie.
And now - having spent the best part of a year wondering what could possibly have led to our favorite Avengers to team up with Cap or Iron Man - we finally know...
Why Each Avenger Chose Their Side in Captain America: Civil War
Now, for the purposes of this discussion, I'm going to assume that every hero taking part in Marvel's 'civil war' is at this point a de facto member of the Avengers, and that any twists and turns in their loyalties that may or may not arise later on in the movie don't affect their initial stance.
Also, if you were wondering when those aforementioned GIANT, HULKING SPOILERS start appearing, that'd be just below...
First up, then?
Captain America's Anti-Registration Gang
Now, Sam 'The Falcon' Wilson can in many ways be considered the most surprising of Cap's allies in Civil War, with his past military service seeming to make him an unlikely rebel. With his loyalty to Captain America well established, however, and his belief in doing the right thing finely honed, Sam ultimately seems to side with Cap via a one-two punch of friendship and morality.
The Winter Soldier
Well, seeing as Iron Man's side - or at least the armed forces attached to it - is trying to kill him, there's really no side Bucky 'The Winter Soldier' Barnes could be on but Cap's. Other than his own, I suppose.
Another hero whose decision to help Cap is perhaps a little unusual, Clint 'Hawkeye' Barton argues that he's helping Cap because he owes it to Scarlet Witch to do so. With his background of determined individualism, though, it seems reasonable to assume that Hawkeye doesn't just come out of retirement to protect the young Avenger - but also out of a sense of doing the right thing, and protecting his friends' freedom to choose their own paths.
Now, the movie sort of skims over Scott 'Ant-Man' Lang's motivation for teaming up with Cap - with the fact that he's pretty anti-authoritarian by nature (and idolizes the Captain a little bit) seemingly outweighing the fact that he's an ex-con whose main superheroing achievement thus far was to blow up a building - meaning he'd be unlikely to catch a break if caught. Could Hank Pym's distrust of all Stark's have played a part in his decision-making, perhaps?
Another Avenger who seemed torn between her mistrust of the idea of registration and her sense of responsibility to the greater good, Wanda 'Scarlet Witch' Maximoff's mind was surely made up the moment Iron Man decided to imprison her in the Avengers compound 'for her own safety'. Add in her lifelong distrust of Tony Stark, and her comparatively warm relationship with Cap, and Wanda's decision makes a whole lot of sense.
And now, somewhat inevitably?
Iron Man's Pro-Registration Avengers
Leading off with...
An endlessly loyal and patriotic military man, James 'War Machine' Rhodes is about the least likely man to betray the US government in the entire MCU. Between that and the fact that Tony Stark's his best friend there was never any real doubt as to which side Rhodey would choose.
Previously a close ally of Cap's, Natasha 'Black Widow' Romanoff seems to have been pulled to Iron Man's side by her own doubts about The Avengers' ability to know what the right thing to do is at any given moment. Having felt betrayed by S.H.I.E.L.D. at the end of Captain America: The Winter Soldier, it's perhaps a little surprising that Natasha was inclined to believe in government infallibility - but perhaps less so when you consider her lifetime of service. Despite being a natural leader, Black Widow has always seemed happiest when operating as part of an organization big enough to quell her doubts about her past activities.
What with The Vision being the product of a Tony Stark-designed A.I. and all, it's not really all that surprising that he ultimately decided to back his partial creator - especially since his other 'father', Ultron, was driven by a flawed version of the same obsession that pushes Stark into battling Cap: The desire to protect the world from itself.
With T'Challa believing that The Winter Soldier killed his father, it's hardly a surprise that he would join a team dedicated to retrieving him in his other role as The Black Panther. Would things have been different had the Wakandan king not been assassinated, though?
Now, as an impressionable fifteen year-old, there's a pretty solid argument that Peter 'Spider-Man' Parker shouldn't have been anywhere near Civil War's battleground - but what nerdy kid would ever turn down a personal invitation from Tony Stark to fight alongside the Avengers? Especially when it seems that the offer came with a shiny new suit design attached...
The big question now, then?