Following the death of Konstantin Chernenko (Andropov's successor) in 1985, Gorbachev was appointed general secretary of the party despite being the youngest member of the politburo. He embarked on a comprehensive program of political, economic, and social liberalization under the slogans of glasnost ("openness") and perestroika ("restructuring"). The nuclear disaster at Chernobyl (1986) forced Gorbachev to allow even greater freedom of expression. The government released political prisoners, allowed increased emigration, attacked corruption, and encouraged the critical reexamination of Soviet history.

In a series of summit talks (1985-88), Gorbachev improved relations with U.S. President Ronald Reagan, with whom he signed an Intermediate Nuclear Forces (INF) arms limitation treaty in 1987. By 1989 he had brought about the end of the Soviet occupation of Afghanistan (see Afghanistan War) and had sanctioned the end of the Communist monopoly on political power in Eastern Europe. For his contributions to reducing East-West tensions, he was awarded the 1990 Nobel Peace Prize. By 1990, however, Gorbachev's perestroika program had failed to deliver significant improvement in the economy, and the elimination of political and social control had released latent ethnic and national tensions in the Baltic states, in the constituent republics of Armenia, Georgia, Ukraine, and Moldova, and elsewhere.

A newly created (1989) Congress of People's Deputies voted in Mar., 1990, to end the Communist party's control over the government and elected Gorbachev executive president. During 1990 and 1991, however, the reform drive stalled, and Gorbachev appeared to be mollifying remaining hardliners, who were disgruntled over the deterioration of the Soviet empire and increasing marginalization of the Communist party. An unsuccessful anti-Gorbachev coup by hardliners in Aug., 1991 (see August Coup), shifted greater authority to the Russian Republic's president, Boris Yeltsin, and greatly accelerated change. Gorbachev dissolved the Communist party, granted the Baltic states independence, and proposed a much looser, chiefly economic federation among the remaining republics. With the formation of the Commonwealth of Independent States (CIS) on Dec. 8, 1991, the federal government of the Soviet Union became superfluous, and on Dec. 25, Gorbachev resigned as president. Since 1992, Gorbachev has headed international organizations; written several books, including On My Country and the World (tr. 1999), and run unsuccessfully (1996) for the Russian presidency. He also heads the International Foundation for Socio-Economic and Political Studies, better know as the Gorbachev Foundation (est. 1991), a think-tank.