The Anti-Ballistic Missile Treaty, also known as the ABM Treaty or ABMT, was a 1972 arms control treaty between the United States and the Soviet Union on the limitation of the anti-ballistic missile (ABM) systems used in defending areas against strategic ballistic missiles, which are used to deliver nuclear weapons. It was intended to reduce pressures to build more nuclear weapons to maintain deterrence. Signed in 1972, it was in force for the next 30 years. Citing purported risks of nuclear blackmail from a rogue state, the United States under the George W. Bush administration unilaterally withdrew from the treaty in June 2002, leading to its termination. In ICBM defense, the US has subsequently operated the Ground-Based Midcourse Defense ABM system based in Alaska and California, as well as the sea-based Aegis Ballistic Missile Defense System. Russia maintains the A-135 ABM system around Moscow, and has developed the S-500 missile system.