The events which led up to this very final fall started during the August coup when hard liners tried to seize control from the Mikhail Gorbachev government. Even though the coup failed the Baltic Republics, long resentful of their forced joining of the Soviet Union by Stalin, declared independence. Negotiations to keep these rogue Baltic states in the union failed. In early December it was decided nationalist feelings were to strong in all the republics and the once feared Evil Empire, to quote Ronald Reagan, was to be no more. The last aspect of the Soviet Union, a flag over the Kremlin, was lowered on December 31, 1991.
The USSR's first encounter with the outside world was war when the World War I allied powers (including a detachment of the United States army) intervened in 1918 to try to stop the Communist rise to power. Until the fall the Soviets and the West were involved in proxy-wars across the globe. Millions of people died in satlitte wars and states that fell into the orbit of the USSR. The legacy of the Soviet Union lasts today. There are a few communist states still left (including "socialist" thugs like in Zimbabwe and Syria) and some people still look to the Marxist ideals for improvement. All because of the empire which collapsed fifteen years ago today.