Alan Scott, a Green Lantern, had played a major role in the JSA's formation. Dr. Manhattan however interfered with their timeline and caused him to die during a train accident by moving the Green Lantern, that had saved his life originally, away from his reach. This caused the JSA to never exist in the first place.
Their past existence was first leaked to Lois Lane secretly by Reggie Long. She however had never heard of them, a result of Dr Manhattan's meddling with the timeline. Superman's words and actions however inspired Manhattan's view on humanity to change and make him realize the importance of being a hero. He went back into time and moved the Green Lantern back into Scott's reach, causing him to survive and the JSA to exist again.
Other results of the undoing of the alterations was that Wonder Woman had fought alongside the JSA in World War II, while Superman had been inspired by the JSA to become a hero much earlier as a teenager by donning the mantle of Superboy. They came to the rescue of Superman in Washington, D.C. alongside the Legion of Super-Heroes, helping him stop the metahuman battle.
After the battle, they vowed to investigate the "Supermen theory", which alleged that the government was secretly creating metahumans to act as agents, and the role of Department of Metahuman Affairs in it. It was discovered that Professor Martin Stein was responsible for creating dozens of metahumans, leading to his arrest. Superman later organized a dialogue between the JSA and People's Heroes, who had been involved in the battle at Washington, D.C.
Current Incarnation:
Justice Society of America (Present Day)
Former Incarnations:
Justice Society of America (World War II)
