Stalin became increasingly harsh as a dictator during his last years. He died in March, 1953. Georgi Malenkov became premier, but Nikita Khrushchev won the vital post of first secretary of the Communist party. Lavrenti Beria, head of the secret police, was initially one of the most important men in the post-Stalin government, but by the end of 1953 his opponents had had him arrested, tried for treason, and shot. Malenkov resigned in 1955 and was succeeded by Marshal Nikolai Bulganin, but Khrushchev was the real ruler. In 1956 Khrushchev denounced Stalin in a speech before the party congress, accusing him of crimes and misrule. This speech was the beginning of a program, called de-Stalinization, of reducing Stalin's stature in the eyes of the Soviet people. In 1958 Khrushchev became premier.

The Soviet Union had suffered enormous destruction in World War II, and in the early postwar years the government drove the people to strenuous efforts to rebuild the economy quickly. Much was accomplished in the Fourth Five-Year Plan, 1946–50, and many industries, especially those producing capital or military goods, matched or exceeded their prewar levels of production by 1953. Under Khrushchev, production of consumer goods was increased in an attempt to satisfy public demand. Khrushchev tried to institute major changes in Soviet agriculture, particularly by emphasizing the growing of corn and the use of previously unplanted land. However, these projects did not significantly help Soviet agriculture.

Soviet progress in space technology became evident in 1957, when the first man-made earth satellites, Sputniks I and II, were put into orbit. In 1961 the Soviet Union sent the first manned satellite into orbit. .

In 1953 Khrushchev restored diplomatic relations with Yugoslavia, which had broken away from the Soviet bloc in 1948, and in 1955 he visited the country. In 1956 the Soviet Union invaded Hungary and brutally suppressed an uprising against that country's pro-Soviet regime.

In 1960 the Soviets shot down an American U-2 spy plane flying high above the Soviet Union. They were infuriated at the violation of their airspace, but meetings with United States leaders helped ease some of the tension between the two countries. New crises were caused by the construction of the Berlin Wall by East Germany in 1961 and the Soviet Union's attempt to install missiles in Cuba in 1962. ( Nonetheless, in 1963 the Soviet Union agreed with other major powers to limit the testing of nuclear weapons.

By the early 1960's, China had begun to reject Soviet leadership of the international Communist movement. In 1963 China denounced the Soviet policy of "peaceful coexistence" with the West and accused the Soviets of being "revisionists," unfaithful to Marxist ideology. From the early 1960's, there were frequent minor clashes between the two nations along their common border.

Khrushchev was deposed suddenly in 1964, after other members of the Politburo lost confidence in his leadership. Leonid Brezhnev, who had been serving as his deputy in the party secretariat, became first secretary of the party. (In 1966 the title was changed back to general secretary, as it had been before 1953.) Under Brezhnev's rule, the de-Stalinization campaign was greatly relaxed.

Brezhnev shared power with Aleksei Kosygin and Nikolai Podgorny. Heavy industry and military production were again given high priority, although production of consumer goods remained higher than it had been under Stalin's rule. Khrushchev's experimental agricultural programs were abandoned. The economy flourished.

In the late 1960's the Soviet government began to increase its harassment and persecution of dissidents. Intellectuals who spoke out against the regime were jailed. Because many of the dissident intellectuals were Jews, Jewish religious activities were restricted by the government. Jewish emigration also was severely curtailed. Worldwide protest resulted in periodic easing of emigration restrictions.

In 1968 a movement for liberal reforms gained widespread support in Czechoslovakia. When the Czech government seemed to be moving away from Soviet-style rule, the Soviet Union reacted by sending troops into Czechoslovakia in August, 1968, to ensure the removal of reform-minded Czech leaders. After this invasion, the Soviets developed the "Brezhnev doctrine," a policy calling for Soviet intervention to halt any developments that might disrupt the Communist order in eastern Europe.

By the early 1970's, the Soviet Union's military power matched that of the United States. In 1972 the Soviet Union and the United States signed the Strategic Arms Limitation Treaty (SALT), in which each country agreed to limit its nuclear missile strength. This agreement contributed to détente, a general relaxation of tensions between the two nations.

In 1975 the Soviet Union was one of 35 nations that signed the Helsinki Accords. These nations agreed to recognize all borders in Europe as inviolate, and also agreed to respect the human rights of their own citizens. The Soviet Union ignored the human rights provisions, and dissidents began to make public their country's violations of the agreement. A period of severe repression followed.

In the late 1970's, growth in the economy declined because of poor central planning and management. In 1979 a second arms limitation treaty, known as SALT II, was signed, but the U.S. Senate refused to ratify it after the Soviet Union installed a puppet government in Afghanistan late the same year and sent in troops to back up the regime. In protest against the Afghanistan invasion, the United States and a number of other nations boycotted the 1980 Olympic Games in Moscow.

By the early 1980's, relations between the United States and the Soviet Union had deteriorated considerably. When martial law was imposed in Poland, the United States government believed that the Soviet Union had urged the Polish regime to take this action. Several trade agreements between American firms and the Soviet Union were cancelled.

Relations with the West continued to decline in 1983 after the Soviets shot down a South Korean commercial airliner that had strayed into Soviet airspace in eastern Asia. In 1984, the Soviet Union led a boycott by several Communist nations of the Olympic Games in Los Angeles.

Meanwhile, there was a period of instability in the top leadership. Brezhnev died in 1982 and was succeeded by Yuri Andropov, a former head of the secret police. He proposed radical economic reforms, but died in 1984 before they could be implemented. Konstantin U. Chernenko succeeded Andropov, but he died 13 months later.

In March, 1985, Mikhail S. Gorbachev became general secretary. He consolidated his power by dismissing many officials and replacing them with his supporters. Gorbachev instituted new domestic policies. Glasnost (openness) encouraged public discussion of Soviet problems as a means of fostering reform; perestroika (restructuring) sought to eliminate ineptitude and corruption within the bureaucracy. Relations with the United States improved, and in 1987 the two nations signed an agreement eliminating their intermediate-range nuclear missiles.

The Soviet Union withdrew its troops from Afghanistan during 1988–89. In 1989 a meeting of senior Soviet and Chinese officials led to improved relations between their nations.

During 1988–89, Gorbachev implemented various governmental reforms that radically altered the way in which the Soviet Union was ruled. He persuaded the Communist party to relinquish its monopoly on political power and to recognize the authority of the new Supreme Soviet and the newly created Congress of People's Deputies. Also, the government created the office of president and vested it with broad executive powers. Gorbachev was elected to that position in 1989.

The government approved a variety of economic reforms aimed at introducing a market-based economy. These measures included the legalization of private businesses and the reduction of state subsidies for many industries. Numerous economic problems followed, including high inflation and shortages of many goods, especially food.

Meanwhile, democratic reform movements arose in eastern European countries and the legitimacy of Communist rule was challenged. Gorbachev rejected the "Brezhnev doctrine" and made little effort to support the Communist governments in these nations. Most of them either collapsed or were reconstituted as democratically oriented regimes with the Communist party in a minor role. Gorbachev's hands-off policy made possible the reunification of Germany in 1990.

Ethnic and nationalist tensions flared up dramatically during 1989–91. Fighting between ethnic groups occurred in Georgia, Azerbaijan, Moldavia (Moldova), and Kirghizia (Kyrgyzstan). The Soviet government responded by sending troops to these regions to restore order.

All 15 union republics proclaimed that their laws took precedence over those of the central government. During 1989–90, Lithuania, Latvia, Estonia, Armenia, Georgia, and Moldavia all declared their intentions to secede from the USSR. The Soviet government did not recognize any independence claims, and in 1990 Soviet troops stormed various communications facilities in Lithuania and Latvia.

In 1991, Gorbachev negotiated a powersharing treaty with most of the union republics. In August, before the treaty was signed, a group of hard-line Communists overthrew Gorbachev and seized control of the government. The coup quickly failed, because of widespread opposition led by Boris Yeltsin, president of the Russian Soviet Federated Socialist Republic, and the failure of key military units to support the coup. Gorbachev was returned to power.

After the failed coup, the Communist party was suspended and its assets were seized by the government. Also, Gorbachev resigned as general secretary. A new, transitional government, designed to give more power to the republics, was established.

Nationalism in the union republics, however, continued to rise. In September, the Soviet government recognized the independence of Lithuania, Latvia, and Estonia. By November, virtually all of the remaining republics had proclaimed their desire to secede from the Soviet Union but to maintain a unified economic community.

On December 8, Russia, Ukraine, and Byelorussia (Belarus) formed a loose confederation known as the Commonwealth of Independent States (CIS). By December 21, all of the remaining republics, except Georgia, had joined the CIS. On December 25, 1991, Gorbachev resigned as president of the Soviet Union, effectively ending the nation's existence.