The Justice League burst onto the scene in 1961, combining the greatest DC heroes. Since then, the Justice League has faced off against the most dangerous threats in the multiverse, teaming up with the heroes of other universes, and basically making sure the sun rises every day for everyone. The Justice League deals with situations that would take entire superhero universes all on their own, with the stakes for failure being ridiculously high.
Source:https://www.cbr.com/justice-league-comics-most-important-events-ranked/