What subtitle does the 2003 film X2 use?

The 2003 film X2 uses the subtitle X-Men United.

The film was marketed as X2: X-Men United and serves as the direct sequel to 2000’s X-Men. Its story brings the heroic X-Men into an uneasy alliance with Magneto and members of his Brotherhood after a mutant-related attack increases government pressure on the mutant population.

The subtitle emphasizes the film’s central idea: rival mutant groups must cooperate against a larger threat. X2 is often informally called simply X2, but “X-Men United” is the official subtitle used in its title. The movie was directed by Bryan Singer and features returning performers Patrick Stewart, Hugh Jackman, Ian McKellen, Halle Berry, Famke Janssen, and James Marsden. It is also notable for expanding the roles of characters such as Nightcrawler and Mystique.