Anti-Ballistic Missile Treaty
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.
Source: Wikipedia — Anti-Ballistic Missile Treaty (CC BY-SA 4.0)