"Nation X" (also known as "X-Men: Nation X") is a 2009–2010 crossover storyline published by Marvel Comics featuring the X-Men. Published in the aftermath of the "Utopia" storyline and dealing with the return of Magneto, the story appeared across several different books, including Uncanny X-Men #515–522, Nation X #1–4 and X-Men: Legacy #228–230. Its writers include James Asmus, Matt Fraction, Grace Randolph, Scott Snyder, Simon Spurrier, and Christopher Yost, and its artists include Leonard Kirk, Mike Allred, Terry Dodson, Greg Land and Whilce Portacio.

The storyline dealt with the aftermath of the "Utopia" storyline and the return of Magneto. Along with the main run in Uncanny X-Men, a four-issue anthology series title Nation X was released along with Nation X: X-Factor one-shot.^{[citation needed]} Additionally, the Deadpool arc "Want You to Want Me" acts as an unofficial tie-in to the main storyline.

Since Deadpool becomes super rich he has no need for being a mercenary and tried to be a pirate, which he soon gave up on. Instead, he decides to help the X-Men on Utopia. Cyclops disagrees instantly, but Deadpool is later put on the team on probation, under the watchful eye of Domino. Deadpool decides to help the X-Men by settling a dispute between Mercury and her father (paid by Norman Osborn to make the X-Men look bad). Deadpool hunts the man down and threatens to kill him only for the man to also be hunted down by H.A.M.M.E.R. Deadpool pretends to be the bad guy and is willingly defeated by the X-Men, making them look like heroes again. Deadpool then leaves, while Cyclops admits that Wade "has some skill".

Shortly after the funeral of Dr. Yuriko Takiguchi on Utopia (previously known as the first Asteroid M), Magneto confronts the new inhabitants of his former home. Magneto stuns everyone by telling them he has come in peace and wishes to speak with Cyclops.

Professor Xavier is unconvinced, believing the entire ruse to be a trap and attacks him telepathically. In spite of this, Magneto does not fight back. Instead, he gets down on his knees and repeats his peaceful intentions. Cyclops orders Xavier to stand down and agrees to talk with Magneto, but keeps Psylocke close by in case Xavier is right. Magneto explains how he and the High Evolutionary restored his powers and his intention to use the process to reverse the Decimation effect. But since the High Evolutionary's equipment was destroyed in the process of repowering Magneto, this is now impossible. He also reveals that he has been in space since then trying to find another way of saving mutantkind, but to no avail. Magneto expresses his admiration to Cyclops for finally doing what he and Xavier could not: uniting mutantkind together. Magneto fears that mutantkind is doomed until Cyclops tells him that Hope Summers, the Mutant Messiah is alive and well. Meanwhile, Scalphunter was recently kidnapped by a group of non-mutant superhumans. They proclaim to want to save all of mutantkind, but force him to fly a plane (which secretly contains five mutant-eating creatures) towards Utopia. Nightcrawler is sent to investigate Scalphunter's intentions as he approaches the island. Upon teleporting to the plane, he retreats to the surface screaming for Cyclops to shoot the plane down before it can land. Cyclops shoots at the plane.

When the five Predator Xs attack Utopia, the X-Men, Namor, and Magneto band together and kill them.

While Professor X helps Cyclops extract the Void from Emma Frost, Magneto helps the X-Men into keeping Utopia from sinking due to the extra weight from the other mutants.

After becoming disillusioned about Cyclops' judgement of having Magneto join up with them, Beast leaves the team.