Five thousand years ago, Darkseid and his legion of Parademons attempted to conquer Earth using the Mother Boxes. The attempt was foiled by a unified alliance of Old Gods, Amazons, Atlanteans, Men and a Green Lantern, and the Mother Boxes unintentionally left behind during their retreat. After the battle, the Boxes were hidden in different locations, guarded by the Amazons, Atlanteans, and Men, respectively. In the present, Superman's death[b] triggers the Boxes' reactivation, attracting Steppenwolf, Darkseid's disgraced lieutenant, to Earth. Steppenwolf aims to regain Darkseid's favor by gathering the boxes to form "the Unity," which would terraform Earth in the likeness of their world Apokolips.

Steppenwolf retrieves a Mother Box from Themyscira, prompting Queen Hippolyta to warn her daughter Diana Prince. Diana receives the message and learns of the events related to Darkseid and Steppenwolf. She informs Bruce Wayne, and the two seek to form a team of metahumans to protect Earth. Bruce locates Arthur Curry and Barry Allen, while Diana locates Victor Stone. Barry joins immediately, while Arthur and Victor refuse. However, Victor joins after his father Silas and several other S.T.A.R. Labs employees are kidnapped by Parademons seeking the humans' Mother Box. When scouts from the Atlantean outpost guarding their Mother Box go missing, having been kidnapped and interrogated by Steppenwolf for its location, Arthur is asked by his mentor Vulko to protect the outpost when his half-brother Orm refuses to do anything. Arthur reluctantly goes to the outpost but ultimately fails to stop Steppenwolf from taking the Box.

The team receives intel from Gotham City Police Commissioner James Gordon, leading them to Steppenwolf's army in an abandoned facility under Gotham Harbor. Although the group rescues the kidnapped employees, the facility is flooded during combat, trapping the team until Arthur arrives and delays the flood so they can escape. Victor retrieves the last Mother Box, which he had hidden, for the group to analyze. Victor reveals the history of the Box and that Silas used the Box to rebuild his body after a car accident. He explains that the Boxes are "change machines" that unfalteringly enforce the will of their master, destroying or restoring to life without bias. The group comes to the realization that they could use the Box to resurrect Superman to help fight Steppenwolf. Meanwhile, the two Mother Boxes in his possession show Steppenwolf a vision of a secret power on Earth, the Anti-Life Equation, which was sought after by Darkseid for countless millennia and initially discovered during his first failed invasion of Earth, only to be lost alongside the Mother Boxes. Steppenwolf then informs DeSaad of the discovery and is then informed by Darkseid to complete his mission as he will arrive on Earth personally afterwards. Barry and Victor exhume Superman's body and place it in the amniotic fluid of the genesis chamber in a Kryptonian ship[c] kept in S.T.A.R. Labs. After Barry activates the Mother Box, an amnesiac Superman is resurrected, immediately attacking the group after Victor's cybernetics target him in self-defense. After soundly defeating the group, Lois Lane, who had been visiting the Superman memorial, arrives just in time to calm Superman down, preventing him from killing Bruce. Together, Lois and Superman leave for his family home in Smallville, where he regains his memories and reunites with his mother, Martha Kent.

While the group is recovering from their bout, Steppenwolf attacks S.T.A.R. Labs and retrieves the last Mother Box. Before Steppenwolf could claim it, Silas manages to supercharge the Box with laser heat at the cost of his own life, allowing Victor to track it by tracing the heat. Without Superman, the five heroes travel to where Steppenwolf aims to unite the Boxes. The team fights their way through the Parademons to reach the Boxes but cannot distract Steppenwolf long enough for Victor to synchronize with the Boxes in order to separate them. Superman arrives and overpowers Steppenwolf, but by the time Victor is ready, the necessary charge created by Barry to allow Victor access to the Mother Boxes disperses after being knocked down by a Parademon, allowing the Boxes to merge to form the Unity, causing a massive explosion that wipes out the team. Barry avoids this fate by entering the Speed Force and runs faster than the speed of light, reversing time and giving Victor the necessary charge that ultimately allows him, along with Superman's help, to separate the Boxes. The heroes kill Steppenwolf and toss his body through a portal to Apokolips. Still, Darkseid reassures his servant DeSaad that despite this setback, he will return to Earth with their fleet to complete his quest now that the location of the Anti-Life Equation has been rediscovered.

After the battle, Bruce, Diana, and Alfred Pennyworth agree to set up a base of operations at the former Wayne Manor. As the team establishes, Diana contemplates about her Amazonian sisters, Barry acquires a job in Central City's police department which impresses his father Henry, Victor is inspired by a message from his father to use his abilities for good, Arthur bids farewell to Mera, and his mentor Vulko as he goes to see his father,[d] and Superman resumes his life as reporter Clark Kent and as protector of Earth.

Lex Luthor, who escaped from Arkham Asylum, is visited by Slade Wilson, to whom Luthor reveals Batman's secret identity. After having a nightmare involving Victor, Barry, Mera, Wilson, the Joker, and an evil Superman in a post-apocalyptic world,[e] Bruce receives a visit from the Martian Manhunter, who previously visited Lois disguised as Martha. He thanks Bruce for assembling the team before saying they will be in contact in preparation for Darkseid's next plans.

https://en.wikipedia.org/wiki/Zack_Snyder%27s_Justice_League
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