Before it was a movie, it was a very different comic

This week, the Marvel Cinematic Universe gets bigger as Captain America: Civil War hits theaters. The world's governments demand stronger control over the Avengers, and Tony Stark (Robert Downey, Jr.), AKA Iron Man, is all for it while Steve Rogers (Chris Evans), AKA Captain America, is not having it. Unfortunately for Steve, his best friend Bucky Barnes (Sebastian Stan), AKA the Winter Soldier, is about to be caught in the middle — even as Spider-Man (Tom Holland) makes his debut in the MCU. But what are the comic book roots of this epic battle between friends and teammates?

In some ways, Civil War started in 1981 with the X-Men story Days of Future Past, by Chris Claremont and John Byrne, which introduced the idea of mutants and superhumans being monitored and controlled by the government to the Marvel Universe. In Uncanny X-Men #181 (1984), the Mutant Registration Act is proposed, and in two issues it becomes U.S. law — requiring that humans born with mutant powers register with the government after they realize their status. The Commission on Superhuman Activities (CSA) is formed to oversee the new law, and over the years, heroes such as Captain America, X-Factor and the Avengers have occasional clashes with the CSA as well as its agents who enforce the Mutant Registration Act, such as Mystique and Freedom Force.

the Superhuman Registration Act is proposed as an expansion of the Mutant Registration Act

In 1990, the Superhuman Registration Act is proposed as an expansion of the Mutant Registration Act, requiring registration from humans who aren't born with the mutant X-gene but still gain enhanced abilities and powers. In Fantastic Four #355 and #366, Reed Richards, leader of the FF, testifies before a congressional committee that this is not needed, as superheroes don't need to be hampered by government oversight, while super-villains are already pursued and punished by the law anyway. Reed also points out that the SRA's definition of "superhuman" is so subjective that several members of congress themselves fall into it.

The committee recommends against the SRA and the matter is dropped. But in 1993, Canada (the Marvel version of it, anyway) passes a similar Super-powers Registration Act. The 2007 series Omega Flight mentions that the law remains in effect and has never resulted in major conflicts between Canadian superheroes (unlike those silly, fight-y Americans).

In 2006, Marvel published comics under the label Road to Civil War, such as Amazing Spider-Man #529-531, where Tony Stark (Iron Man) informs Peter Parker (Spider-Man) that congress is once again considering the Superhuman Registration Act, and now also requires registration from humans who only have "powers" due to use of advanced or "exotic" technology. It's still an incredibly subjective definition for a world where Reed Richards, Tony Stark, Hank Pym and other geniuses have made certain sci-fi tech standard issue equipment for many agencies, groups, and personal friends. If someone borrows the Human Torch's shirt, would they have to register since all of his clothing is made of unstable molecule fabric?

The SRA is tabled and barring a change in public opinion, it will keep being set aside until it's gone

In any event, Tony testifies to the Senate that hampering superheroes with government oversight instead of letting them do their job until they prove they're dangerous is a bad idea. Secretly, Tony hires a super-villain to stage an attack on his own life, knowing that Spidey will save him. During their battle, the villain (as per Tony's instructions) tells Spidey that foreign governments believe the SRA will lead to the US imprisoning many of its most powerful defenders, leaving the country defenseless. Tony then shows a recording of these statements to the Senate as proof that the SRA will cause more harm than good, while Spider-Man argues that the whole reason many superheroes exist is to respond to situations that local and federal law enforcement don't or can't respond to. The SRA is tabled yet again and Tony reassures Spidey that, barring a massive change in public opinion on superheroes, it will keep being discussed and set aside until it's finally gone. Of course, right after that, something happens to sway public opinion.

This is the TOC title Civil War

The New Warriors were introduced as a team of college age heroes in the 1990s. In Civil War #1 in 2006, we see the remaining New Warriors performing for a reality TV show, hoping to capture villains for the cameras. But one villain, Nitro, has enhanced his abilities, and delivers a blast that not only kills several of the heroes but also wipes out the surrounding area, resulting in the deaths of 612 people in Stamford, CT, including children.

The "Stamford Incident" convinces many that superhumans need to be trained, regulated and accountable to the government whether they like it or not — whether they even want to be a superhero or not. If you have enhanced abilities and don't feel like being a hero or villain, you're still too dangerous to be allowed to walk around freely. So the Superhuman Registration Act is discussed again, with some superheroes now concerned that secret identities and powers/weaknesses will be recorded into a hackable database, while others argue this is necessary, pointing out that some heroes have worked with public identities and as government agents without having their lives ruined or compromising their principles.

The "Stamford Incident" convinces many that superhumans need to be trained, regulated and accountable

In Civil War, SHIELD is put in charge of enforcing the SRA. At this time, Nick Fury is underground for having defied the US government, so the agency is under the direction of Maria Hill (played by Cobie Smulders in the Marvel movies), who tells Steve Rogers, Captain America, that he's to take down any superhero who defies registration when the SRA becomes law. Cap refuses to imprison friends and colleagues because of their biological traits and adds that he objects to registration himself, so Hill orders her agents to attack him — which seems extreme and illegal, since the SRA isn't law yet. Naturally, Cap escapes and starts recruiting a new "Secret Avengers" team made of heroes who oppose registration and wish to continue just doing what they do best, even if they have to sometimes fight off SHIELD agents.

Meanwhile, Tony Stark now openly supports the SRA and reveals to the world that he's Iron Man (not the first time he's done this but ... comics!). A couple of weeks later, it becomes law and Tony leads a new officially-sanctioned Avengers team to stop not only super-villains but also unregistered heroes. Tony convinces Spider-Man to also support the SRA and unmask to the public, as Spidey has simultaneously been one of the most famous and secretive superheroes in the Marvel Universe. Peter does so, which leads to attacks not only by super-villains but also from people in his personal life who now seek to sue him for various reasons.

Things get darker as the weeks go on. Superhumans against registration are imprisoned in another dimension without trial. Tony tells Peter Parker that superhumans who don't register are legal non-entities and can remain imprisoned for the rest of their lives if they refuse to comply (wait, really, Tony?). Super-villains already incarcerated are released under supervision to hunt down unregistered superheroes.

Captain America refuses registration and forms the Secret Avengers

With Thor currently absent from Earth (due to Asgard being temporarily gone), Tony authorizes the creation of a very aggressive clone of Thor (later called Ragnarok, though some readers call him "Clor"). It's revealed that Tony collected DNA samples of Thor after the Avengers were first founded and kept them for years, just in case (wow, what the hell, Tony?). The clone isn't as powerful as Thor, so Tony gives it cyborg enhancements to compensate and I guess to increase the whole Frankenstein feel of it.

Tony then lures Cap and his Secret Avengers into a trap, telling them they have another chance to surrender and just register already. Cap agrees to discuss things with Tony, but this is a lie and he sets off a secret weapon to mess with the Iron Man armor (what the Hell, Steve, since when can we not take Captain America at his word?). A brawl ensues and the Thor cyborg-clone is unleashed on the Secret Avengers, killing Bill Foster, Giant-Man.

Meanwhile, it turns out that trusting super-villains to enforce the law can lead to bad things! Some villains use brutal methods in enforcing the SRA, while Norman Osborn, the Green Goblin, attacks Atlanteans and nearly provokes a full-out war between the US and Atlantis. Osborn, however, doesn't seem to be in control of his actions and doesn't know why he attacked Atlanteans.

These events, and others, cause Spidey to seriously reconsider his position, especially when he also realizes that the high-tech spider-suit Tony recently gave him not only monitors his body and powers, but also allows him to be controlled if he steps out of line (what the hell, Tony?). When Spidey says he's done with fighting fellow heroes, Tony attempts to take control of him via the suit and is surprised to realize Peter has already disabled that feature. Spidey joins Cap's side.

More battles happen. Tony and Steve both have spies working in the other guy's camp. King T'Challa of Wakanda, the Black Panther, sees the SRA as the beginning of a new superhuman arms race, leading to a conflict with Tony and a later battle where the cyborg-clone Thor destroys the Wakandan embassy in a rage. The Black Panther chooses to support Captain America's side.

Under pressure from civilians, the Secret Avengers concede and surrender

Finally, during a big battle, several civilians and emergency workers tackle Captain America, asking him to stop because these fights endanger bystanders. Steve concedes and surrenders, on the condition that any of his Secret Avengers who now decide to register will be offered amnesty for defying the SRA up to this point. Stark agrees. Some heroes still decide to defy the SRA, including Spidey, who adopts his old black costume again to reflect the darker attitude he's developing due to all the bad things going on — and because the movie Spider-Man 3 was coming out and would also feature a version of the black costume.

Meanwhile, Tony Stark takes over SHIELD and a new "50-State Initiative" is launched, putting a government employed superhero team in every state, while untrained and young superhumans will now undergo special training at Camp Hammond, named after the original Human Torch Jim Hammond (arguably Marvel's first true superhero) and built in Stamford, CT. In the pages of the Civil War tie-in Frontline, it is revealed that Stark has been playing a long game with the 50-State Initiative as the end goal.

It's actually Stark who, behind the scenes, manipulated Congress to start talking about the SRA again, at which point he pointed out it could be restructured so it wouldn't weaken the country against foreign attacks, then took advantage of the Stamford Incident to make sure there was pressure to make it law as quickly as possible. He also manipulated the stock market, forced Norman Osborn to attack Atlanteans, and did other things all so that the government and he could organize superheroes into an efficient, united force spread out across the entire USA, one that could stand against any attack from foreign or alien powers — even if it meant he had to compromise his principles, force people to act against their free will, and be considered a traitor by many friends. Though a couple of reporters discover this, they decide not to go public as it could unravel the good they believe Tony Stark has done.

As Steve Rogers is being taken to stand trial for his crimes, he is shot by Crossbones (you saw him in Captain America: Winter Soldier and will see him again in Captain America: Civil War) and then shot again by his hypnotized friend and on-again, off-again love interest Sharon Carter (who is portrayed by Emily VanCamp in Winter Soldier and Civil War). He's pronounced dead minutes later and the world now sees him as a martyr for the anti-SRA side. Looking over Steve's body, Tony concludes that the Civil War wasn't worth all the pain it caused and the lives lost.

Captain America is assassinated

Steve's old partner Bucky Barnes becomes the new Captain America for some time, even after it's revealed that Steve isn't really dead but is locked in a time travel loop (because comics). Steve later returns but tells Bucky to remains Captain America. Bucky does so, until he then dies in battle (except that turns out to not be real either), leading to the original taking up the role again.