Thousands of years ago, Steppenwolf and his army of Parademons attempted to takeover Earth with the combined energies of three Mother Boxes. They are foiled by a unified army that included the Olympian Gods, Amazons, Atlanteans, mankind, and the Green Lantern Corps. After repelling Steppenwolf's army, the Mother Boxes are separated and hidden in locations around the planet. In the present, the world is in mourning over Superman, whose death triggers the Mother Boxes to reactivate and Steppenwolf's return to Earth in an effort to regain favor with his master, Darkseid. Steppenwolf aims to gather the artifacts to form "The Unity", which will destroy Earth's ecology and terraform it in the image of Steppenwolf's homeworld.

Steppenwolf manages to retrieve the Mother Box from Themyscira, prompting Queen Hippolyta to warn her daughter Diana of Steppenwolf's return by lighting the invasion fire. Diana joins Bruce Wayne in his attempt to unite other metahumans to their cause, with Wayne going after Arthur Curry and Barry Allen, while Diana tries to locate Victor Stone. Wayne fails to persuade Curry, but manages to recruit an enthusiastic Allen onto the team. Although Diana fails to convince Stone to join, he agrees to help them locate the threat if he discovers their location. Stone later joins the team after his father Silas, along with several other S.T.A.R. Labs employees, are kidnapped by Steppenwolf seeking to acquire the Mother Box from mankind.

Steppenwolf attacks Atlantis to retrieve the next Mother Box, forcing Curry into action. The team receives intel from Commissioner James Gordon leading them to Steppenwolf's army, based in an abandoned facility under Gotham Harbor. Although the group manages to rescue the kidnapped employees, the facility is flooded during combat, which traps the team until Curry helps delay the flood so they can escape. Stone retrieves the last Mother Box, which he had hidden, for the group to analyze. Stone reveals that his father used the Mother Box to rebuild Stone's body after an accident almost cost him his life. Wayne decides to use the Mother Box to resurrect Superman, not only to help them fight off Steppenwolf's army, but also to restore hope to mankind. Diana and Curry are hesitant about the idea, but Wayne forms a secret contingency plan in case Superman returns as a nemesis.

Clark Kent's body is exhumed and placed in the incubation waters of the Kryptonian ship alongside the Mother Box, which in turn activates and successfully resurrects Superman. However, Superman's memories have not returned, and he attacks the group after Stone accidentally launches a projectile at him. On the verge of being killed by Superman, Batman enacts his contingency plan: Lois Lane. Superman calms down and leaves with Lane to his family home in Smallville, where he reflects and tries to recover his memories. With the final Mother Box unguarded, Steppenwolf retrieves it with ease. Without Superman to aid them, the five heroes travel to a village in Russia where Steppenwolf aims to unite the Mother boxes once again and remake Earth. The team fights their way through the Parademons to reach Steppenwolf, although they are unable to distract him enough for Stone to separate the Mother boxes. Superman arrives and assists Allen in evacuating the city, as well as Stone in separating the Mother Boxes. The team defeats Steppenwolf, who, overcome with fear, is attacked by his own Parademons before they all teleport away.

In the aftermath of the battle, Bruce and Diana agree to setup a base of operations for the team, with room for more members. Diana steps back into the public spotlight as a hero; Barry acquires a job in Central City's police department, impressing his father; Victor continues to explore and enhance his abilities with his father in S.T.A.R. Labs; Arthur returns to Atlantis; and Superman resumes his life as reporter Clark Kent. In a post-credits scene, Lex Luthor escapes from Arkham Asylum and recruits Slade Wilson to form their own league.

https://en.wikipedia.org/wiki/Justice_League_(film)
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