relaxed as well. Khrushchev's reforms in agriculture and administration, however, were generally unproductive. In 1962, he precipitated a crisis with the United States over the Soviet deployment of nuclear missiles in Cuba. An agreement was made with the United States to remove nuclear missiles from both Cuba and Turkey, concluding the crisis. This event caused Khrushchev much embarrassment and loss of prestige, resulting in his removal from power in 1964. Era of Stagnation (1964–1985) Following the ousting of Khrushchev, another period of collective leadership ensued, consisting of Leonid Brezhnev as general secretary, Alexei Kosygin as Premier and Nikolai Podgorny as Chairman of the Presidium, lasting until Brezhnev established himself in the early 1970s as the preeminent Soviet leader. In 1968, the Soviet Union and Warsaw Pact allies invaded Czechoslovakia to halt the Prague Spring reforms. In the aftermath, Brezhnev justified the invasion and previous military interventions as well as any potential military interventions in the future by introducing the Brezhnev Doctrine, which proclaimed any threat to socialist rule in a Warsaw Pact state as a threat to all Warsaw Pact states, therefore justifying military intervention. Brezhnev presided throughout détente with the West that resulted in treaties on armament control (SALT I, SALT II, Anti-Ballistic Missile Treaty) while at the same time building up Soviet military might. In October 1977, the third Soviet Constitution was unanimously adopted. The prevailing mood of the Soviet leadership at the time of Brezhnev's death in 1982 was one of aversion to change. The long period of Brezhnev's rule had come to be dubbed one of ‘standstill’, with an ageing and ossified top political leadership. This period is also known as the Era of Stagnation, a period of adverse economic, political, and social effects in the country, which began during the rule of Brezhnev and continued under his successors Yuri Andropov and Konstantin Chernenko. In late 1979, the Soviet Union's military intervened in the ongoing civil war in neighboring Afghanistan, effectively ending a détente with the West. Perestroika and Glasnost reforms (1985–1991) Two developments dominated the decade that followed: the increasingly apparent crumbling of the Soviet Union's economic and political structures, and the patchwork attempts at reforms to reverse that process. Kenneth S. Deffeyes argued in Beyond Oil that the Reagan administration encouraged Saudi Arabia to lower the price of oil to the point where the Soviets could not make a profit selling their oil, and