Technically, this war began millennia ago when Darkseid and his armies first arrived on Earth and battled against a united force of Amazons, Old Gods, a Green Lantern Corps member, Atlanteans, and the tribes of Men.
The conflict ended in 2017 when Steppenwolf and his armies attempted to invade Earth under Darkseid's orders. However, Steppenwolf was defeated and slain by the Justice League at the Battle of Pohzarnov.
During the first invasion over 5,000 years ago, the mighty ruler of planet Apokolips, Darkseid, arrived to conquer the Earth, and he faced the united armies of Humans, Amazons and Atlanteans altogether the Old Gods and one Green Lantern sent by the Guardians of Oa for help in defending Earth against Darkseid.
He had used the Mother Boxes for transforming the Earth and murdered a Green Lantern in the process, but he was defeated by Zeus and forced into retreat, leaving the Mother Boxes in the process and returning to Apokolips in humiliation.
It is believed that when Darkseid learned of Superman and his death after Luthor contacted Steppenwolf, Darkseid sent his general to obtain the mother boxes in his name and thus began the next invasion shortly after.
The Second Invasion
In the present, the world is in mourn following the death of Superman. Sensing the Call of the Mother Box, Steppenwolf and his Parademons return to Earth to resume their hunt for the Mother Boxes through kidnapping several employees of S.T.A.R. Labs, which is in possession of one of the boxes.
Steppenwolf manages to retrieve the Mother Box from Themyscira, prompting Queen Hippolyta to warn her daughter Wonder Woman. She joins Batman's group and informs him about Steppenwolf and the Mother Boxes. The two of them fail to persuade Aquaman and Cyborg, but manage to recruit Flash into the team. Cyborg later joins the group after his father Silas Stone is among those kidnapped, and Steppenwolf attacks Atlantis to retrieve the second Mother Box.
The Justice League vs. Steppenwolf
The team later receives intel from Commissioner James Gordon that the Parademons are traveling underground, and conclude that Steppenwolf's army is based in an abandoned facility. Although the group managed to rescue the kidnapped employees, the facility is flooded during combat, which traps the team until Aquaman rescues them, having decided to join them after Steppenwolf's attack on the Atlanteans.
Cyborg retrieves the last Mother Box from S.T.A.R. Labs for the group to analyze. Batman decides to use the Mother Box to resurrect Superman not only to help them fight Steppenwolf's army, but also to restore hope in humanity. Wonder Woman and Aquaman are hesitant about the idea, but Batman forms a secret contingency plan.
Clark Kent's body is exhumed and placed in the waters of the Kryptonian ship, and Allen provides a strong energy blast to activate the Box and resurrect Superman. Superman, however, possesses few memories, and he attacks the group after Cyborg 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 Lois to his family home where he reflects and tries to recover his memories. With the last Mother Box unguarded, Steppenwolf retrieves it with ease.
The Final Battle
Without Superman to aid them, the remaining five heroes travel to a remote location in Russia called Pozharnov, where Steppenwolf plans to unite the boxes and terraform the world for his lord and master.
The team fights their way through the Parademons to reach Steppenwolf, although they are unable to stage a significant enough distraction for Cyborg to separate the boxes. Superman arrives and assists Flash in evacuating the city, and ultimately aids Cyborg in separating the Mother Boxes.
Following the separation, an enraged Steppenwolf is caught off guard by Aquaman, who impales the New God through the chest. After Superman punches Steppenwolf towards the Boom Tube, Wonder Woman beheads him in mid-air, killing him. His corpse lands on Apokolips In front of Darkseid, who stomps on his head and breaks off his remaining horn before glaring at the Justice League as the Boom Tube closes.
After DeSaad tells Darkseid that he knew Steppenwolf would fail his duty, Darkseid calmly agrees before ordering DeSaad to prepare the Apokolipitian Armada, intending to invade Earth using the "old ways".
After the war ended, the members of the Justice League went their own ways again, but vowed to defend the Earth. They are hailed by the general public as international heroes, with merchandise created in their honor. The Wayne Manor was also selected to be remodeled as the headquarters of the Justice League.
In chronological order:
- Terrio, Chris, Whedon, Joss (writers) & Snyder, Zack (director) (November 17, 2017). Justice League.
- Goyer, David S., Terrio, Chris (writers) & Snyder, Zack (director) (March 25, 2016). Batman v Superman: Dawn of Justice.
- Bernstein, Abbie and Johns, Geoff (November 21, 2017). Justice League: The Art of the Film. Great Britain: Titan Books.