Détente, French for “relaxation,” is “a process of managing relations with a potentially hostile country in order to preserve peace while maintaining our vital interests,” Henry Kissinger, then U.S. secretary of state, told a Congressional committee in 1974, while warning that such a relationship faces “sharp limits.”

Despite early nuclear arms agreements such as the 1963 Limited Test Ban Treaty that came in wake of the Cuban Missile Crisis, the Vietnam War escalated tensions between the U.S. and Soviets, while anti-war protests and domestic pressures mounted.

But with both countries facing large economic impacts related to the arms race and military spending, along with the Sino-Soviet split, there was a strong incentive by both parties to ease geopolitical relations and undergo arms control discussions.

Soon after Nixon’s landmark visit to China in February 1972, he began a series of meetings with Brezhnev, then general secretary of the Soviet Communist party, where, according to the Richard Nixon Foundation, mistrust bloomed into a friendship.

The first U.S. president to visit the Soviet Union since 1945, Nixon and Brezhnev, took part in three breakthrough historic summits while both held office, first in May 1972, followed by Brezhnev’s visit to Washington in June 1973 and a return trip to Moscow by Nixon in June/July 1974, which totaled 100-plus hours.

“I felt that the relationship between the United States and the Soviet Union would probably be the single most important factor in determining whether the world would live at peace during and after my administration,” Nixon wrote in his memoirs.

Earlier arms accords, including the 1963 Partial Test Ban Treaty and 1968 Nuclear Non-Proliferation Treaty, helped set the ground for future détente agreements. Started in 1967 between President Lyndon B. Johnson and Soviet Premier Alexi Kosygin, the Strategic Arms Limitation Talks (SALT), continued by Nixon and Brezhnev at their 1972 summit, eventually led to the signing of the SALT I treaty. The agreement limited the number of intercontinental ballistic missiles (ICBMs) either side could have in their arsenals and allowed each nation to build two missile defense sites.

The 1975 Helsinki Final Act followed. Signed by 35 nations at the Conference on Security and Cooperation in Europe, it focused not only on military issues and defining political borders, but also advanced opportunities for increased trade and scientific cooperation and promoted cultural exchanges, human rights and freedom of the press.

After years of negotiations between Presidents Gerald Ford and Jimmy Carter and Brezhnev, Carter and the Soviet leader agreed to and signed SALT II negotiations in 1979, which established an equal number of nuclear weapons between the countries and limited MIRV missiles, among other guidelines.

But with the 1979 Soviet invasion of Afghanistan, Carter delayed ratifying it, as did Brezhnev, although both agreed to uphold the treaty.

With the continued arms talks stalled and tensions between the U.S. and Soviets rising following the invasion, the détente era was deteriorating.

“While this invasion continues, we and the other nations of the world cannot conduct business as usual with the Soviet Union,” Carter said during his January 23, 1980, State of the Union address, announcing stiff economic penalties on the Soviet Union, a ban on permits for Soviet ships to fish in U.S. coastal waters, the cutting off of access to high-tech and agricultural products and other trade limitations. “And I have notified the Olympic Committee that with Soviet invading forces in Afghanistan, neither the American people nor I will support sending an Olympic team to Moscow.”

Carter’s support of Afghan and Pakistani troops and America’s boycott of the 1980 Moscow Olympics, followed by the 1980 election of Ronald Reagan who referred to détente as a “one-way street that the Soviet Union has used to pursue its aims” and, in 1983 called the nation an “evil empire,” ended the détente era as the Cold War escalated once again.

"Nixon and Brezhnev – Partners in Détente," Richard Nixon Foundation.

"The Cold War, 1961-1972," BBC Bitesize.

"Détente and Arms Control, 1969–1979," Office of the Historian, U.S. Department of State.

“Detente: A History of Ups and Downs in U.S-Soviet Ties,” The New York Times.