TO UNDERSTAND Crisis, a little history of both the DC universe and our own is in order.
In the real world, DC Comics first came to prominence in the 1940s, when hundreds of new heroes from dozens of comic companies joined Superman (1938) and Batman (1939) in the fight against evil. This so-called "Golden Age" was the greatest creative era in comics history. After the Second World War, most comic publishers saw less profit in superheroes, and public opinion against the supposed corrupting influences of fictional vigilantes meant an end to most superhero careers. By the early 1950s, Superman, Batman and Wonder Woman were virtually the only ones left to continue their adventures.
In 1956, DC brought back the Flash, but he was not the Flash older readers remembered. This new Flash was a young police scientist named Barry Allen who named himself the Flash in honor of his comic-book hero, the original Flash.
In Flash #123, writer Gardner Fox brought the two Flashes together in a story that would have huge repercussions on the DC universe. The new Flash accidentally transported himself to another dimension, a place where everything is the same except that the new Earth was home to all the 1940s DC heroes that he once read about in comic books on his world. We learn that "Earth-1" (the new Flash's Earth) and "Earth-2" (the old Flash's Earth) both exist on separate dimensional planes; they're the same, but slightly different. This story paved the way for all the other Golden Age heroes to re-introduce themselves into the DC Universe; Superman-1 (who isn't married and works at the Daily Planet) met Superman-2 (who married Lois Lane and works at the Star), Batman-1 (a younger, single Bruce Wayne) met Batman-2 (an older, married Bruce Wayne), and so on.
DC knew it had a winner on its hands when the sales figures were tallied. New heroes could be introduced to the younger readers while older readers could enjoy their childhood favorites. Justice League of America soon hosted an annual team-up between the JLA and the Justice Society of America, and books such as the All-Star Squadron and Infinity, Inc. appeared in the early 1980s to introduce DC's Golden Age heroes to a new generation of comic readers.
But there were problems. DC's creators began to explore the other versions of Earth that could exist in the multiverse: Earth-3 was home to a villainous version of the JLA... Earth-S was home to the Captain Marvel family... Earth-X was a planet where the Nazis won the Second World War... and so on. As heroes kept hopping from Earth to Earth to defeat their enemies, it got confusing trying to keep track of who was from which earth. Also, by the early 1980s it was clear that DC had to update its biggest stars, but 50 years of history stood in the way. It was time, DC decided, to do a little housecleaning...
COUNTLESS EONS AGO, in the DC universe, the race that would eventually evolve into the Guardians of the Universe (the blue-skinned commanders of the Green Lantern Corps) had already become one of the universe's most advanced civilizations. The Maltusians explored every avenue of science but one: Ancient writings forbade them from exploring the origins of the universe.
One scientist, Krona, dared to defy that rule. He constructed a machine that allowed him to peer back through time to the moment of Creation. Just as the answer was about to be revealed to him, a tremendous explosion ripped through his lab. The shockwaves from that explosion were the beginnings of the "multiverse" -- the splitting of the universe into countless duplicates, each on a different vibrational plane and each slightly different from the rest. It also marked the beginning of the "anti-universe," a place of immense evil and the total opposite of everything the universe embodied.
Ashamed of Krona's folly, the future Guardians agreed to shoulder the responsibility for containing evil in the universe. They punished him for his transgression, created the Green Lantern Corps to become their cosmic police force, and did their best to contain the evil unleashed by Krona's folly.
Then one day, the multiverses started to disappear...
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