When Jack Kirby began his work on the Fourth World at DC, one of the core tenets of the mythology he was creating was that the new did not invalidate the old, as so often happens when writing about God or gods. Rather, the New Gods literally replaced that which had come before them.
"There came a time when the Old Gods died," declares one splash page, depicting a scene seemingly out of Ragnarok. We have previously speculated that such a battle -- and the death of the old gods -- might usher in an age of New Gods, setting the stage for the events of the Justice League movie.
"Back before history, mankind, the Atlanteans before they were underwater, the Amazonians (sic), and actually the Old Gods, teamed together and decided that, based on an event that happened, these Mother Boxes were going to be" divided between the three non-god groups, Justice League executive producer Charles Roven previously said.
And then the last of those old gods -- Ares, who had fled from the battle that apparently killed the rest after being seriously injured in a fight with Zeus -- died at the end of Wonder Woman... and that film's recently released "epilogue" reveals that a Mother Box, theoretically the one left in the care of mankind, was unearthed after some bombings in World War I and needed to be recovered and delivered to the Americans.
It seems likely that the Mother Box in question is the same one seen in Batman v Superman: Dawn of Justice, which helped create Cyborg.
Following Superman's death in that movie, Batman visits Lex Luthor in prison, and Luthor warns him that "out there, among the stars," someone has heard a bell, joking, "Ding-dong, the god is dead." Given the frequent references to Superman as a "god" in that film, it is reasonable to assume that Luthor is talking about Superman's death, but it could just as easily be that he is talking about the death of Ares.
The deleted scene in which Lex can be seen looking at Kryptonian records dealing with Steppenwolf and the New Gods took place either prior to or, at most, during the death of Superman, so the notion that the New Gods could learn that Earth is "defenseless" without him and that Lex would know that and understand the gravity of what he learned has always seemed a little far-fetched.
What Lex appeared to be looking at were "files" about the New Gods' connection to Earth, which given the Roven quote above, likely dealt with how they were repelled by humans, Atlanteans, Amazons, and old gods. While Lanterns and Kryptonians were referenced in the second trailer for Justice League, it is likely they were an afterthought, and that their absence only underscores how the deaths of the old gods leaves Earth ripe for new ones.
"[New Gods creator Jack] Kirby was crazy and a great guy, and there's a lot of influence, you know? Sort of New Gods stuff, and we were digging on that," said Justice League director Zack Snyder. "That's the Mother Boxes and that Apokoliptian world and all that stuff. You can't really do that stuff without some... I don't know if I'd call it weird; larger than life, kind of scope-y, sci-fi, cool, but I think it's fun stuff."
If one were to assume this theory has any kind of credibility, it might also explain why Wonder Woman was the film that took place between Batman v Superman and Justice League: if the events of Wonder Woman directly inform the plot of Justice League, setting the solo movie after the team-up would inherently spoil the film's ending a little bit. On the other hand, while Atlantean mythology will play into Justice League, there is no clear indication that the story they want to tell in the Aquaman movie will suffer as a result.