What kind of story does The Avengers tell?

The Avengers is mainly about a sudden powerful evil force, which poses a fatal threat to the earth, and no superhero can resist it alone. S.H.I.E.L.D., which has been committed to safeguarding the safety of the earth, was caught off guard. Nick Farley, its commander, realized that he had to create the strongest alliance ever, and gather superheroes from all sides to show off their strength, so as to save the world from suffering and resist the invasion of the dark forces. So The Avengers came into being.