Twentieth Air Force was reactivated on 1 September 1991 as a component of Strategic Air Command and located at Vandenberg AFB, California. Its mission was the responsibility for all land-based Intercontinental Ballistic Missiles (ICBM)s. 20th Air Force's rebirth came at a time when America's nuclear forces were entering a decade of unprecedented force reductions and changes. Spawned by the Cold War's end and the breakup of the Soviet Union, these changes reshaped the basic fabric of the nation's nuclear deterrent forces.