1:Eventually the citizens of Vault City tired of having their groundwater radiated by the ghoul's leaking atomic reactor in Gecko.
2:In a wave of xenophobic fear and hatred, the well-armed soldiers of Vault City slaughtered the peaceful ghouls and shut down the reactor for good.
3:Unable to harness any additional sources of power Vault City eventually stagnated and died-itself a victim of it's own hatred.