The Underground was assembled by Cable after rumors spread of mutants being snatched from their homes in the middle of the night, never to be heard from again. The Underground was a large network of mutants coordinated by Cable's private council of operatives who uncovered the existence of the Weapon X Program and their Neverland concentration camps. Cable was defeated by the program when he tried to confront them, however, his team's memories altered to believe Weapon X had been destroyed.
Marrow took the opportunity to seize control of Cable's Underground network after he abandoned it, turning it into a new Gene Nation under her control, following Weapon X (2nd series) #13.
