Few superhero teams can match the power and prestige of DC's Justice League. The team regularly faces cosmic villains and threats to the fabric of reality itself, yet always manages to walk away victorious. However, one of DC's darkest futures saw the League crumble, and all because of a surprising hero.
With powerhouses like Superman, Wonder Woman, and Martian Manhunter, it's no wonder that the League is basically undefeatable. Even in universes where the League does disband, it's less often due to a crushing defeat, and more due to internal squabbles. Classic comics such as Kingdom Come show a League unable to reconcile their different views of justice, while more recent alternate universes such as Justice League: Last Ride see the team breakup due to misplaced blame. While not unheard of, it's rare for the team to take a loss so hard that it destroys them. Yet, Dick Grayson once delivered a blow so devastating, that the League never recovered.
In Kyle Higgins and Trevor McCarthy's Nightwing: The New Order, a war breaks out between the heroes and villains of DC's universe. Centered on Metropolis, the war grows and grows, as does its body count. A turning point eventually comes when black kryptonite is used on Superman, making the Man of Steel kill Batman. With grief in his heart and no end for the war in sight, Nightwing has no choice but to act. He uses a piece of technology from Apokalips that erases 90% of the world's superpowers. Left powerless, the Justice League and their foes lay defeated, their newfound vulnerability catching up to them. Though Superman does live through the experience, the lack of heroes such as Wonder Woman, Barry Allen, Aquaman, and Shazam later on hints that Dick's choice resulted in the deaths of many heroes.
It's no understatement to say that Dick destroyed the Justice League, even if some may have survived. After the battle for Metropolis ends, superpowers are outlawed, with Dick leading the force that rounds up those who retained their abilities. The group of heroes that resist Nightwing's fascist state isn't the League, but a much older group of Teen Titans, with the addition of Blue Lantern Lois Lane. What makes the destruction of the League all the more tragic is that it was Dick Grayson who caused all of it. Nightwing is the DC Universe's greatest triumph, a beacon of hope in a dark world, so to see him end the world's greatest defenders is heart-wrenching.
Far from a moment created purely for shock value though, Dick's betrayal of the League makes total sense in context. While Nightwing: The New Order ultimately decides superpowers are good, it's easy to see why Dick made the choice that he did, especially given Batman's death. Still, there's something incredibly ironic about a group as powerful as the Justice League being taken down by a hero without powers like Nightwing.