10 Justice League Movie Plot Predictions
6. Tensions Between Atlanteans & Amazons Play A Huge Part
If the prologue rumours are to be believed, then the Atlanteans and Amazons teamed up with humanity to repel Darkseid, but since then their relationship has soured heavily, especially as each side likely possessess one of the Mother Boxes (and the third ended up in humanity's hands, leading to Cyborg's creation).
It just makes so much sense that both sides would wish to possess all of the Mother Boxes given their immense power, and this would lead to a Cold War of sorts between the two factions, as each is aware that the other could unleash a Mother Box upon them.
From there, it seems probable that the human touch is what will eventually convince the Atlanteans and Amazons to reluctantly team up once again to take on Steppenwolf. This conflict will probably account for most of Willem Dafoe's screen time as Aquaman's political advisor Nuidis Vulko.