Fall of the Soviet Union By mg17317 Period: Aug 25, 1979 to Dec 25, 1992 . Dec 25, 1979 USSR enters war with Afghanistan Jan 20, 1981 Reagan becomes president Mar 23, 1983 Strategic Defensive Initiative enacted Mar 11, 1985 Gorbachev becomes General Secretary of the Communist Party Apr 12, 1985 Glasnost and Perestroika are introduced Apr 26, 1986 Chernobyl nuclear accident Dec 8, 1987 INF Treaty is signed Feb 15, 1989 The last Soviet troops leave Afghanistan Nov 9, 1989 Berlin Wall falls Aug 10, 1991 500 Day Plan enacted Dec 25, 1991 All remaining Soviet states secede from the USSR