Earth-X is so evil it doesn't have a number. It is a reality where the Nazis won.
According to Harrison Wells, Earth-X is technically the 53rd Earth in the Multiverse, but has never been given an official numerical designation as the atrocities committed on this Earth are so horrific that the other Earth's in the Multiverse would rather pretend that it didn't exist.
The Nazi Germany developed the Atomic Bomb before America did. As a result, Germany used their newfound weapon of mass destruction to nuke New York City, London, Paris and Moscow which resulted in the Allied Forces' defeat thus ending World War II with Nazi Germany's victory.
- Nazi Party
- Freedom Fighters
- This is the first reality shown that contains alternate versions of characters from both Earth-1 and Earth-38.
- This earth is based on elements of Earth-X, Earth-10, and Earth 10
- In the Supergirl episode Worlds Finest, Barry Allen mention the concept of the Multiverse including an Earth where the Nazi won World War II which could of possibly foreshadowed the idea of Earth-X’ existence. 
- Characters from Arrowverse: Earth-X
- Other things related to Arrowverse: Earth-X
- Arrowverse: Earth-X's Comic Appearances
- Reality Gallery: Arrowverse: Earth-X
Links and References