Several Earths were hypothesized throughout DC Comics' history. Initially, "our" Earth was that of the golden age heroes of the Justice Society, then in more modern times "our" Earth became that of the Justice League. Even later, it was speculated that our true Earth had to be a hero-less world to match that which was reality, although any fictional characters would have real world counterparts. Such was the case when writer Cary Bates interjected himself in a tale of the Flash meeting Earth-One's scarlet speedster. After each traveled to the others world, with Cary's being Earth-Prime, this new world became the template for the reader's world itself.
Midway through the run of Justice League/Society crossovers, a story was produced that screamed of running out of ideas, when Bates and Elliott S Maggen found themselves via Flash's cosmic treadmill on Earth-Two and Earth-One. Bates was quickly transformed into a powerful villain by the Wizard, and a plot was afoot to cause the Injustice Society for once to become the victors over their heroic counterparts of Earth-Two.
Another plot years later had Earth-Prime's newly introduced first superhero Ultraa who migrated from his world to Earth-One, and causing all kinds of headaches at a time when the Injustice Gang under the auspices of a mysterious hooded power broker was manipulating matters behind the scenes, sending his five minions to retrieve four objects of tremendous power!
Each Injustice team had six members, with the hooded leader of the Gang later revealed as Abra Kadabra while the Society's leader was the Wizard. Each team had a guy who produced a variety of gimmick gadgets, Tattooed Man and Sportsmaster, and two femme fatales, Poison Ivy and the Huntress. Each had a teleporting Flash foe, Mirror Master and the Shade; gun wielding crook, Chronos and Icicle; and a Gotham City criminal, Scarecrow and the Gambler.
Added to the mix was the intervention of the aforementioned Ultraa and Bates. With the best of intentions, Ultraa zapped the League with a negative though inducing device that neutralized the heroes while Bates setup a trap that ultimately neutralized the Society. Both teams seemed in the final battle with their enemies to be demoralized and near their wits end when the encouragement of their fellow heroes motivated them towards victory. With Bates banished back to his home world along with his fellow writer, and Ultraa imprisoned until a future tale, the threats of Injustice and Earth-Prime waned from that point. Yet a remarkable parallel of twice-told-tales remained to be chronicled in the pages of the Justice League of America.
As a side note, the intervention of the Justice League on Earth-One to help defeat the Injustice Society on Earth-Two was later mirrored when the Johnny Thunder of Earth-One recruited the six Crime Champions to pillage his Earth which prompted the visiting Justice Society of Earth-Two to battle the villains. On each Earth, only with the awakening of each world's native heroes was their sufficient numbers to defeat each sinister six. And on each case, Johnny Thunder and Black Canary were present. Yet another twice-told-tale!