Ant-Man & the Wasp is arriving at a somewhat unusual time in the Marvel Cinematic Universe. Although the film is the first to arrive after the cataclysmic events of Avengers: Infinity War and takes place concurrently with that movie, Thanos' activities aren't expected to have a large impact on the film. Instead, it's the fallout from 2016's Captain America: Civil War that looms large over Ant-Man & the Wasp, with that film's Sokovia Accords being addressed in a big way. So how do the Sokovia Accords work, and what do they have to do with Ant-Man?
If it's been a while since you've seen the movie, the main conflict at the center of Civil War was a multinational government agreement known as the Sokovia Accords. The Accords were adopted following the carnage that took place during the battle between the Avengers and Ultron in the Eastern European country of Sokovia in 2015's Avengers: Age of Ultron. The battle left the nation decimated, and many around the world blamed the Avengers for the destruction. As a result, a treaty of sorts was drawn up by 117 countries that takes away the right of the Avengers to operate freely without government oversight. Instead, they would be overseen by a panel at the United Nations and deployed only when that panel sees fit.
In Civil War, Iron Man was in favor of signing and abiding by the Accords, as he felt guilty and thought the Avengers should be held accountable for their actions. Captain America, on the other hand, was fresh off of uncovering a Hydra conspiracy at the heart of the U.S. Government, and he didn't trust turning over the keys to the Avengers to political operatives who have their own agendas, so he opposed signing the Accords. Each hero had several other heroes side with them, which resulted in a physical fight between the two camps. Ant-Man sided with Captain America, meaning he sided against the government and broke the law by acting as a superhero outside of the parameters set forth in the Accords. In doing so, he ended up being arrested and agreeing to a sentencing of house arrest so he could be with his daughter. This is why he, along with Hawkeye, was missing from Infinity War, and in Ant-Man & the Wasp, he's been under house arrest — and prevented from being Ant-Man — for two years.
Marvel Studios head Kevin Feige recently revealed a bit more about the major impact the Accords had on Ant-Man, AKA Scott Lang, as he had more to lose than the other heroes who rebelled against the Accords. "The notion of [Ant-Man & the Wasp] was always to be a relative standalone film that took into account (the fact that) what was a fun cameo in Civil War, was really a giant deal and a big sacrifice for [Scott Lang] in his real life in his relation with his daughter, and his relationship with Hank and Hope, and this guy whose entire first movie was about becoming a good guy and coming out of prison and trying to make the right life for himself, which he did and he became a hero," Feige told comicbook.com's Brandon Davis. "He answered a call when heroes needed him and now he's been under house arrest for two years."
At their core, the Sokovia Accords prevent superheroes from being superheroes without government approval and direction. Presumably, this means that both Ant-Man and the Wasp are acting as vigilantes in Ant-Man & the Wasp, and both heroes could face some serious repercussions from the government if they end up being caught doing their hero thing in the film.