The Justice League Never Would Have Existed Without The Sandman
The heroes of the Justice League may have the central protagonist of The Sandman to thank for their team's creation. A chain reaction throughout the DC Universe that led to the formation of a team of the Earth's most notable protectors began the moment Dream of the Endless manifested into the world.
In the team's long history, the way the Justice League first came together has changed over time. The earliest origin of the League saw the crew come together when White Martians attempt to invade the planet, while a revamped origin in the New 52 had the heroes unite to create an alliance when Darkseid's forces come to Earth. Of course, they wouldn't be the first united group of heroes in the DC Universe. Depending on the continuity, the Justice Society is shown to be one the biggest influences on the modern team of heroes.
To that end, Sandman #1 by Neil Gaiman, Sam Keith, and Mike Dringenberg adds a new layer to the history of both teams of heroes. The series starts with industrialist Roderick Burgess attempting to capture Death but accidentally capturing Death's brother, Morpheus the Lord of Dreams, instead. Dream, as he is also known, is held captive for decades, and his absence has a significant impact on the world. Sleep disorders plague humanity, with some people going to sleep for years and others ceasing to sleep at all. The story even acknowledges the effect it has on Wesley Dodds, the Sandman of DC's Golden Age. Nightmares begin to plague Dodds, until he finds peace by donning his superhero gear and venturing out to fight crime.
It's certainly not a coincidence that the sleep that finally comes to Dodds is called the "Sleep of the Just." While Dream's removal is presented as an overall negative to the world, his absence helps create one of DC's most well-known Golden Age heroes. The Sandman would go on to become a member one of the first superhero teams with the Justice Society. And though originally the Justice Society and Justice League were on two separate Earths, the post-Crisis continuity (which The Sandman was set in shortly after the era was established) merged the two worlds so that the Society was active decades before the League came together.
Now, is it fair to say that if Dream hadn't been captured, there wouldn't have been a Justice Society or a Justice League for that matter? Perhaps not, as the team had a number of other significant heroes such as Flash, Green Lantern and the Spectre. But the events of The Sandman show that Dream's removal helps usher in a new age of heroes. The "Sleep of the Just" that Dodds finds may come knowing that a new era is dawning and that other heroes like him are out there. Dodds may not know it, but his dreams will lead him to joining up with a team that will inspire one of the largest collections of heroes his world had ever seen. Though the first act of The Sandman begins tragically, Dream's capture kickstarts a wave of heroism that would ultimately end with the creation of the Justice League.