Détente was a period in which Cold War tensions eased between the Soviet Union and the United States from the late 1960s to 1979. Détente was characterized by warm personal relationships between US president Richard Nixon (1969–1974) and Soviet leader Leonid Brezhnev (1964–1982). Détente led to the series of summits between the leaders of two superpowers and the signing of number of international treaties such as the Partial Test Ban Treaty (1963), the Nuclear Non-Proliferation Treaty (1968), the Anti-Ballistic Missile Treaty (1972), and the Helsinki Accords (1975), that served as the groundwork for the Organization for Security and Cooperation in Europe (OSCE). Détente ended after the Soviet invasion of Afghanistan in 1979. In Russian, the term razryadka is used for détente.