. . . in the early 1970s, when DC tended to publish a series of issues/books known as "
100 Page Super-Spectaculars" which were filled with reprint material, DC started including reprints of some of the Quality Comics heroes along with those originally published by DC.
And then, in the summer of 1973, for the annual meeting of Earth-1's
Justice League of America and Earth-2's
Justice Society of America, DC decided to bring several of Quality Comics' Golden Age superheroes into the DC universe by placing them on an yet another alternate Earth . . . one where the Nazis had been the victors of World War II!