The newest Justice League trailer officially introduced fans to the DC Extended Universe's Steppenwolf, the general from Apokolips who will attack Earth with his Parademon army. Along with being a fierce warrior, Steppenwolf also has the sinister monologuing down pat, and one of his more intriguing lines in the preview was when he mentioned that Earth doesn't have any Lanterns to protect it. Any person even casually familiar with DC Comics will instantly recognize that as a reference to the Green Lanterns, the intergalactic police force introduced during the Silver Age of comics. The Green Lantern Corps reboot is set to give the emerald-tinted mythology a second chance at big screen fame, but Steppenwolf's name drop seems to indicate that during the events of Justice League, the Green Lantern of Sector 2814 is either dead or missing in action.
For those not familiar with the Green Lantern mythology, the DC universe is divided into 3600 sectors, and each sector has at least one Green Lantern to patrol it, although in recent years the standard number of Lanterns per sector has been raised to two. Earth rests in Sector 2814, and before Hal Jordan became the first human member of the Green Lantern Corps in the comics, our sector was protected by Abin Sur. Right now, it's unclear what Earth's Green Lantern situation is when Justice League rolls around.
On the one hand, Green Lantern Corps is expected to be a buddy cop movie between Hal and John Stewart, with Hal presumably being the more experienced Lantern like in the comics. On the other hand, it's been rumored that Abin Sur will cameo in Justice League, meaning that a human Green Lantern hasn't been assigned yet. Either way, it's hard to imagine the Guardians of the Universe, the founders and leaders of the Green Lantern Corps, being negligent and not having a Green Lantern watching over Earth. Just because humanity has only known about alien life for a few years doesn't mean that one of the Emerald Knights wouldn't protect the planet if something threatened to harm it.
So then what's going on with Justice League? Our best guess is that either before the movie or early into the story, the Green Lantern of Sector 2814 has either been "dealt with" or is "occupied elsewhere," to use as loose of terms as possible. If the Green Lantern who is supposed to look after that sector is an alien, then they're most likely dead, as DC wouldn't risk killing off one of the human Green Lanterns so soon. If the Green Lantern is Abin Sur, then his demise could potentially serve as an adaptation of Hal Jordan's origin. Abin Sur tries to stop Steppenwolf from reaching Earth, and is fatally injured in the process. From there, the ring selects its new wielder within that sector, and whether Hal gets to meet Abin Sur like he did in the comics and the 2011 Green Lantern movie or doesn't come face to face his predecessor, he would be transported to Oa for training, hence why a Green Lantern isn't aiding Batman, Wonder Woman, Aquaman, Flash and Cyborg in battling Steppenwolf and the Parademons.
However, if we assume that Hal Jordan or another human has been serving as the Green Lantern of Earth for some time, then that person is likely just missing in action somehow. Maybe Steppenwolf defeated them, but stopped short of killing them. Maybe Hal and/or John are dealing with a different emergency in Sector 2814, and by the time they learn about the assault on Earth and return home, the crisis has been averted. Of course, one would think that foiling an invasion from Apokolips would jump to the top of their to-do list, but hey, maybe they're evacuating a planet or dealing with an equally massive undertaking.
A more shocking possibility is that the Green Lantern Corps has been destroyed. There is precedence for that, as in the mid-1990s, Hal Jordan was corrupted and became Parallax during the "Emerald Twilight" arc, where he singlehandedly toppled the Green Lantern Corps, leaving Kyle Rayner and later John Stewart to carry on the Green Lantern legacy for the next decade. Perhaps something happened in the DCEU that led to the Green Lantern Corps' collapse, and the Green Lantern Corps movie will follow the organization beinf rebuilt. However, Steppenwolf's phrasing in the Justice League trailer only indicates that Earth is without a Green Lantern, not that the entire universe is without the shining green light of willpower. So things may not be dire for the entire Corps...yet.
Given the underwhelming performance of the first Green Lantern movie, DC and Warner Bros are taking their time with re-introducing the Green Lantern mythology to the general public. For now, there hasn't been official confirmation of any kind of direct Green Lantern appearance in Justice League, so Steppenwolf's line may be the only Lantern reference we get in that movie. That said, it was reaffirmed during the Warner Bros Hall H presentation at Comic-Con that Green Lantern Corps is one of the top priorities for the DCEU in the coming years, so it's only a matter of time before we delve into that corner of the DC universe. Until then, humanity will have to put its faith in this newly-formed superhero team to repel the alien invaders.
We'll hopefully learn more about the status of the Green Lanterns in the DCEU when Justice League hits theaters on November 17. Green Lantern Corps is expected to arrive in the summer of 2020.