The superheroes of the MCU exist in a morally and legally ambiguous state, simultaneously appearing to be military personnel operating with the backing of the state and also violent vigilantes taking matters into their own hands. In fact, S.H.I.E.L.D.--the organization which helped found the Avengers--seems to both represent US national interests and international peacekeeping efforts. Considering the messy situations that the Avengers get into, it is not surprising that they have had to make some tough decisions.
Unfortunately, there have been times they did not handle things well and even engaged in war crimes, whether they knew it or not. A detailed breakdown of just what constitutes a war crime would take far too long than can be adequately explained in full, but there are some activities which clearly are in violation of international law. Unfortunately, while the Avengers have saved the world, some of the MCU's heroes have done things that should hypothetically have them tried in the Hague.
Warning: Wandavision Spoilers Below
10 Iron Man Invaded A Country And Offered No Quarter To People He Killed
The MCU began with 2008’s Iron Man, a film where Tony Stark is described as “the Merchant of Death.” As an arms manufacturer, it is a fitting description for him.
Even when he sought to become a hero by donning the Iron Man suit, he couldn’t help but spread death, as seen when he invaded a country and began killing people without offering them any quarter. These militants took hostages who could have been killed. Additionally, given his lack of training, he almost certainly made things worse by killing a bunch of people in a warzone without any intel about the situation on the ground. A key part of Tony's character at this point is his naivete of the complexities of modern warfare.
9 Bucky Barnes Assassinated A Bunch Of Innocent People
After being subjected to horrible brainwashing experiments, Bucky was turned into a living weapon, known as the Winter Soldier.
In this capacity, he killed political figures, scientists, and independent government contractors. He even murdered Tony Stark’s parents. This is a big difference between killing enemy combatants and sniping people to serve a political agenda.
8 Sam Wilson, Natasha Romanoff, And Steve Rogers Kidnapped And Tortured A Non-Combatant Government Official
In Captain America: The Winter Soldier, Steve learned that Hydra had infiltrated S.H.I.E.L.D. In response, he, Natasha Romanoff, and Sam Wilson kidnapped Agent Jasper Sitwell to interrogate him, as he appeared to be part of Hydra.
Then, they threw him off the roof of a building. Of course, Sam caught the man at the last minute, flying him back up- trying to scare him into a confession. This could be considered as a form of psychological torture, and it was done on the mere suspicion that Sitwell might be part of Hydra.
7 Wanda And Pietro Maximoff Assisted In Attempted Genocide
By allying with Ultron, Wanda and Pietro Maximoff were complicit in his attempt at genocide. Actually, that is only partially true. See, genocide is the extermination of a specific group of people. This is why ethno-nationalist movements have targeted specific ethnic, religious, and gender minorities for genocide.
Ultron wanted to wipe out pretty much all biological life on Earth. Cockroaches and a few other creatures would survive, but they would be the exception. In other words, Wanda and Pietro helped someone who was attempting a crime so severe genocide does not even begin to accurately describe it.
6 Wanda Blew Up A Building With A Suicide Bomber
To be clear, this was not Wanda’s fault. When the Avengers cornered Brock Rumlow (AKA Crossbones) as he attempted to detonate a bomb on his person, he was in the middle of a crowded market at the time.
In an act of desperation, Wanda telekinetically hurled Rumlow into the air. The bomb exploded, killing people in a nearby building. In other words, she was complicit in the deaths of people killed by this suicide bombing. She technically saved the people in the market, but those who did die were killed because of her actions.
5 Iron Man Recruited Spider-Man To Be A Child Soldier
Tony Stark has always been an impulsive bully willing to do anything to get his way. When he and Steve were fighting over the Sokovia Accords, he recruited Peter Parker to help.
Except Tony could not just ask. He threatened to reveal the secret of Peter’s identity to his aunt. In other words, Tony Stark bullied, threatened, and coerced Peter into fighting as a child soldier against Hawkeye (a trained spec ops agent), three combat veterans (one of whom was Captain America), and the telekinetically-powered Scarlet Witch. Using child soldiers is definitely a war crime.
4 Black Widow Has Red In Her Ledger
At this time, Black Widow’s film is still months’ from being released. The film will no doubt reveal some of the concrete details about her backstory and expand on the secret history of the MCU.
What is known at this time is that Natasha Romanoff has “red in her ledger” and that she was trained by the Russians’ Red Room to become an expert assassin, interrogator, and spy. Considering how easily she can kill without batting an eye, it is difficult to imagine just what horrible things she could be ashamed of. In Avengers, Loki referenced a few, dropping such details as “Dreykov’s daughter,” Sao Paolo, and a hospital fire.
3 Hawkeye Committed Multiple Extrajudicial Executions As Ronin
After the blip killed his family, Hawkeye took up a new identity as Ronin. He traveled all over the world, executing criminals. His family was dead, so he had nothing to lose and could not accept that a world could allow evil to exist after the loss of all that was good in his life.
The problem with this is that executing people without trial is illegal, and doing it as a series of surgically precise strikes using his S.H.I.E.L.D. training basically makes this an illegal one-man military operation.
2 Iron Man Replicated Thanos’s Snap
When Thanos snapped his fingers to create the blip, he wiped out half of all life in the universe. Mass murder like that is about the closest thing there is to being unequivocally and objectively evil.
When fighting Thanos in Avengers: Endgame, Iron Man snapped his fingers while wearing his own Infinity Gauntlet, wiping out Thanos’s entire army in one instant. While not as bad as wiping out half of life in the cosmos, this was still a war crime. He gave them no chance to surrender and did not consider who might be coerced into joining Thanos (as some likely were, given how he treated his daughters). When Thanos used the gauntlet, it was evil. This was no less true when Tony committed mass murder with a snap of his own fingers.
1 Wanda Took Over The Town Of Westview And Tortured Its Inhabitants
It is difficult to know just how to classify what Wanda did when she took over the town of Westview in WandaVision.
Torturing and kidnapping civilians are both war crimes. By invading a town, cutting it off from the world, and oppressively mind-controlling the people within it, she violated both national and international human rights laws. These people were subjected to constant psychological torment, while their children were locked away from sight. Wanda never meant to hurt anyone, which makes this even more tragic, but that does not negate the suffering she caused.