Justice League tells about the gathering of DC superheroes ranging from Batman (Ben Affleck), Superman (Henry Cavill), Aquaman (Jason Momoa), Flash (Ezra Miller), and Wonder Woman (Gal Gadot). They unite against an alien criminal who wants to destroy the Earth, namely Steppenwolf.
The Justice League film tells about the mission of Bruce Wayne aka Batman and Diana aka Wonder Woman to gather superheroes to prevent Steppenwolf’s evil intentions from destroying the earth.
Thousands of years ago, Darkseid and his Parademon tried to conquer Earth using the Mother Box after learning that Earth harbored the Anti-Life Equation. The attempt was thwarted by an alliance of the Old Gods, the Amazons, Atlantis, humanity, and the Green Lantern.
After the battle, the Mother Box is hidden in different locations, each guarded by the Amazons, Atlantis, and Humans. In the present day, after Superman’s death (which occurred in Batman v Superman: Dawn of Justice), it triggers a reactivation of the Mother Box, attracting Steppenwolf, the commander of Darkseid’s forces, to Earth.
Steppenwolf aims to regain Darkseid’s support by gathering the squares to form “Unity”, which will reshape Earth in the form of their world Apokolips. Steppenwolf retrieves the Mother Box from Themyscira, prompting Queen Hippolyta to warn her daughter Diana Prince (Wonder Woman). Diana receives a message and learns of events related to Darkseid and Steppenwolf.
He told Bruce Wayne (Batman). Bruce and Diana try to form a team of metahumans to protect Earth. Bruce finds Arthur Curry (Aquman) and Barry Allen (Flash), while Diana finds Victor Stone (Cyborg).
After possessing two Mother Boxes, Steppenwolf attacks S.T.A.R. Lab and take the last Mother Box to put them together. The superheroes also tried to face Steppenwolf and his army but faced failure until finally the revived Superman arrived and helped them.