The Soviet era of Russia history began in 1917 and ended in 1991. The Union of Soviet Socialist Republics (USSR) was not formally declared until 1922, following the Bolsheviks' victory in the Russian Civil War (1918-1920). Although Russia was technically only one component of USSR, which encompassed other "republics," such as Georgia and Armenia, the USSR included virtually all the territory of tsarist Russia, and "Great Russians" remained the dominant ethnic group. A significant exception to this rule was Joseph Stalin, who was Georgian-born.
From the Revolution to the Great Purge
The Bolsheviks were a Marxist revolutionary party that parted ways with more moderate socialist groups in the early 1900s. During the 1920s and early 1930s, the Bolsheviks struggled to impose their policies on the often recalcitrant Russian populace, sometimes with tragic results. Their efforts to collectivize the peasantry were bitterly resisted, leading to millions of deaths by starvation and execution.
V.I. Lenin led the party through the revolution and the early 1920s. After his death in 1924, a power struggle ensued, with the primary opponents being Leon Trotsky and Stalin. Though considered less brilliant than Trotsky, Stalin proved to be a superior politician and administrator. He eventually outmaneuvered Trotsky and other prominent "Old Bolsheviks" to become leader of the party. The power he wielded in this position did not make him feel secure, however; in the mid- to late 1930s, Stalin destroyed anyone he considered a threat, including most of the pre-revolutionary generation of the party. Millions of rank-and-file party members and ordinary Soviet citizens were persecuted and killed during this period, too, often for arbitrary reasons. Many who were not killed outright were sent to forced-labor camps in remote parts of Russia, known as gulags.
The Great Patriotic War
Stalin's purges, which extended to the officer corps of the Red Army, left the country ill-prepared for the German invasion of June 1941, especially as this attack betrayed a nonaggression pact the two countries had signed in 1939. The Germans' blitzkrieg tactics allowed them to quickly overrun huge swaths of Soviet territory, soon putting them within striking distance of Leningrad (formerly St. Petersburg) and Moscow. Behind the lines, special German units murdered millions of Jews, Soviet commissars, and members of other targeted groups.
Eventually, though, the German advance stalled. Despite tremendous losses, the Soviets were able to regroup, moving industrial production safely out of the Germans' reach. Like Napoleon's 1812 invasion forces before them, the Germans were not equipped for the harshness of the Russian winter. With the aid of supplies delivered by the Western Allies, the Soviets pushed back against the Germans, gaining the upper hand by 1943. The Red Army took Berlin in April 1945, ending World War II in Europe - remembered in Soviet history as the Great Patriotic War.
The Cold War
The Soviets occupied and communized most of Eastern Europe after the war. The physical and cultural divide between the democratic, capitalist West and the Communist East became known as the Iron Curtain, and was symbolized most poignantly by the Berlin Wall, which divided Germany's former capital in two. This state of affairs lasted for nearly the remainder of the Soviet Union's existence.
Stalin died in 1953, to be succeeded by Nikita Khrushchev. In 1956, Khrushchev denounced his predecessor, "de-Stalinizing" the Communist Party in the Soviet Union and abroad. However, in this year, the Soviets also crushed a pro-democracy movement in Hungary. A similar crackdown occurred in Czechoslovakia in 1968.
Tensions with the United States rose and fell during the 1950s, 1960s, and 1970s, but never erupted into armed conflict. A period of relatively open relations between the superpowers ended with the Soviet invasion of Afghanistan in 1979 and the election of US President Ronald Reagan the following year, who by increasing US defense spending forced the Soviet Union to do the same. Both of these developments had a negative effect on the Soviet economy.
Decline and Dissolution
From 1982 to 1985, the Soviet Union experienced a succession of elderly party leaders who died in office: Leonid Brezhnev, Yury Andropov, and Konstantin Chernenko. After this, however, a younger, more reform-minded man came to power: Mikhail Gorbachev. His policies are usually known by the terms glasnost (openness or transparency) and perestroika (restructuring). Gorbachev also loosened the Soviet Union's hold on Eastern Europe by withdrawing large numbers of Soviet troops in the late 1980s. This led to the end of Communist rule in those countries in 1989-91, and to the reunification of Germany.
Though popular abroad, Gorbachev met with resistance at home. In August 1991, hard-line elements in the military and the intelligence community (KGB) attempted a coup. It was thwarted by Boris Yeltsin, president of the Russian republic, who rallied the people of Moscow to Gorbachev's support. This preserved Gorbachev's official position, but crippled him politically.
When the various Soviet republics declared their independence in late 1991, they met with only weak resistance from Moscow. In December, Gorbachev resigned, and the Soviet Union ceased to exist.
("Union of Soviet Socialist Republics," Encyclopedia Britannica)