There isn't much known about the history of Genosha other than the fact that it was never touched by Ultron, presumably because it had been destroyed prior and he thought it useless. Because of this Emma Frost, Kitty Pryde, Beast, and X-23 led most of the mutants they could to Genosha and raised them their for years. It wasn't until the Avengers showed up and told them X-Men that the rest of the world was safe did they consider moving out. After Franklin fixed everything, The X-Men left Genosha and moved back to Westchester.
