As National Security Adviser under Nixon, Kissinger pioneered the policy of "détente" with the Soviet Union, seeking a relaxation in tensions between the two superpowers. As a part of this strategy, he negotiated the Strategic Arms Limitation Talks (culminating in the SALT I treaty) and the Anti-Ballistic Missile Treaty with Leonid Brezhnev, General Secretary of the Soviet Communist Party. Negotiations about strategic disarmament were originally supposed to start under the Johnson Administration but were postponed in protest upon the invasion by Warsaw Pact troops of Czechoslovakia in August 1968.