Avengers: Infinity War

The supervillain Thanos comes from a planet called Titan whose people are all dead because of overpopulation. To prevent the same thing from happening to other worlds, Thanos decides to kill half of all living beings on every planet in the entire Universe. To do that, Thanos tries to find six Infinity Stones and bring them together in a glove called an Infinity Gauntlet so that he can make anything he wants to happen with a snap of his fingers.

Thanos gets an Infinity Stone called the Power Stone by destroying the planet Xandar. He gets an Infinity Stone called the Space Stone by striking a deal with Loki in exchange for not killing Thor, killing Loki in the process, He steals the Reality Stone from the Collector; he gets the Soul Stone in exchange for killing his daughter Gamora. He strikes a deal with Dr. Strange to get the Time Stone in exchange for not killing Iron Man.

Because Thor lost his hammer to his half-sister, he, Rocket and Groot go to a dying star to make a new weapon that will stop Thanos. Thor creates Stormbreaker, the best weapon Thor has had in the MCU so far.

Thanos leads an alien invasion of Earth to get the Mind Stone from the robot superhero Vision by killing him. The Avengers, Spider-Man, Black Panther and the Guardians of the Galaxy (Rocket and Groot later help along with Thor who later joins) all work together to stop Thanos.

Thanos eventually steals the Mind Stone and snaps his fingers. He causes half of all living beings on every planet in the entire Universe to disappear from existence.

There is a scene after the credits where Nick Fury successfully tries to signal someone (later revealed to be Carol Danvers/Captain Marvel) who can do something about it but he gets killed by Thanos's snap.