Earth-X

Earth-X is one of the many universes in the multiverse. On this Earth, the Nazi organization won World War II. Due to its horrific state, it doesn't have a formal designation. No sane individual has willingly traveled to this Earth.

History
During World War II, the Nazis won the second World War after nuking New York, London, Paris, and Moscow. Additionally, they set up outposts throughout Europe and the Americas.

Residents

 * Tommy Merlyn/Prometheus (Earth-X) (deceased)
 * Oliver Queen/Dark Arrow (Earth-X)
 * Kara Zor-El/Overgirl (Earth-X)

Visitors

 * Eobard Thawne/Reverse-Flash
 * Oliver Queen/Green Arrow
 * Barry Allen/Flash
 * Sara Lance/White Canary
 * Martin Stein/Firestorm
 * Jefferson Jackson/Firestorm
 * Kara Zor-El/Supergirl
 * Alex Danvers

Behind the scenes

 * In DC Comics continuity, the Nazis play the same role on Earth-X as they do in the shared multiverse. However, it is considered a part of the main 52 multiverse, rather than something outside of it, with its alternate versions in the continuity being known as Earth-10 and Earth 10.
 * There is a number of universes considered to be outside the main 52 universe in the comics, most recently the Dark Multiverse: an amalgamation of "minus universes" born out of people's fears, regrets and nightmares, doomed to disintegrate and be superseded by the new "minus Earths".