The Justice League United was a Canada-based superhero team. The fifth team to use the Justice League moniker, the JLU was different from the likes of the Justice League of America or the Justice League International as it was not sponsored by any outside group. It was more similar to the original Justice League and the Justice League Dark where it was an independent group that acted not under the orders of a governmental organization and fought for heroism. Despite this, as the original League and Team Dark had both at one point been sponsored by ARGUS, the JLU was the first League created that fought for the united cause of heroism. Founded after the Trinity War and the ARGUS Insurgency, many members of the JLU had previously been present in the Justice League of America.
In Toronto, Canada, Animal Man and Stargirl attended a convention together to meet their fans. There they were approached by Adam Strange, who requested help in finding Alanna Lewis. The three headed to the site where she disappeared, but were attacked by aliens. During the attack, they were joined by Green Arrow and the Martian Manhunter, the latter of whom assumed command. Finding the alien base below them, they were attacked by a hybrid creature. During this fight, Adam gained his armour and weaponry. While fighting the hybrid, they were teleported to Rann. The alien base was then found by Miiyahbin Marten where she was attacked by the Whitago. On Rann, the hybrid was captured by the Rannians while Supergirl joined up with the heroes. There, from the Rannian Sardath, they learned of the Ultra Project and of the involvement of Byth Rok. Arriving on the Moon of Thalsalla, the team confronted Byth Rok but were too late to stop Ultra the Multi-Alien from awakening. While Adam Strange, Byth, Hawkman and Ultra the Multi-Alien were teleported back to Ranagar, the others were sent to the outskirts of the city. While Supergirl fought Byth, the Manhunter managed to convicne Ultra to join him.