Soviet Union
On 30 December 1922, Lenin and his aides formed the Soviet Union, by joining the Russian SFSR into a single state with the Byelorussian, Transcaucasian, and Ukrainian republics. Eventually, internal border changes and annexations during World War II resulted in a union of 15 republics, the largest and most populous being the Russian SFSR, which dominated the union politically, culturally, and economically.
Following Lenin's death in 1924, a troika was designated to take charge. Eventually Joseph Stalin, the General Secretary of the Communist Party, managed to suppress all opposition factions and consolidate power in his hands to become the country's dictator by the 1930s. Leon Trotsky, the main proponent of world revolution, was exiled from the Soviet Union in 1929, and Stalin's idea of Socialism in One Country became the official line. The continued internal struggle in the Bolshevik party culminated in the Great Purge.
Under Stalin's leadership, the government launched a command economy, industrialisation of the largely rural country, and collectivisation of its agriculture. During this period of rapid economic and social change, millions of people were sent to penal labour camps, including many political convicts for their suspected or real opposition to Stalin's rule, and millions were deported and exiled to remote areas of the Soviet Union. The transitional disorganisation of the country's agriculture, combined with the harsh state policies and a drought, led to the Soviet famine of 1932–1933, which killed 5.7 to 8.7 million, 3.3 million of them in the Russian SFSR. The Soviet Union underwent a rapid and costly transformation from a predominantly agrarian economy into a major industrial power.
The Soviet Union entered World War II on 17 September 1939 with its invasion of Poland, in accordance with a secret protocol within the Molotov–Ribbentrop Pact with Nazi Germany. The Soviet Union later invaded Finland, and occupied and annexed the Baltic states, as well as parts of Romania. On 22 June 1941, Germany invaded the Soviet Union, opening the Eastern Front, the largest theatre of World War II.
Eventually, some 5 million Red Army troops were captured by the Nazis; the latter deliberately starved to death or otherwise killed 3.3 million Soviet POWs, and a vast number of civilians, as the "Hunger Plan" sought to fulfil Generalplan Ost. Although the Wehrmacht had considerable early success, their attack was halted in the Battle of Moscow. Subsequently, the Germans were dealt major defeats first at the Battle of Stalingrad in the winter of 1942–1943, and then in the Battle of Kursk in the summer of 1943. Another German failure was the Siege of Leningrad, in which the city was fully blockaded on land between 1941 and 1944 by German and Finnish forces, and suffered starvation and more than a million deaths, but never surrendered. Soviet forces steamrolled through Eastern and Central Europe in 1944–1945 and captured Berlin in May 1945. In August 1945, the Red Army invaded Manchuria and ousted the Japanese from Northeast Asia, contributing to the Allied victory over Japan.
The 1941–1945 period of World War II is known in Russia as the Great Patriotic War. The Soviet Union, along with the United States, the United Kingdom and China were considered the Big Four of Allied powers in World War II, and later became the Four Policemen, which was the foundation of the United Nations Security Council. During the war, Soviet civilian and military death were about 26–27 million, accounting for about half of all World War II casualties. The Soviet economy and infrastructure suffered massive devastation, which caused the Soviet famine of 1946–1947. However, at the expense of a large sacrifice, the Soviet Union emerged as a superpower.
After World War II, according to the Potsdam Conference, the Red Army occupied parts of Eastern and Central Europe, including East Germany and the eastern regions of Austria. Dependent communist governments were installed in the Eastern Bloc satellite states. After becoming the world's second nuclear power, the Soviet Union established the Warsaw Pact alliance, and entered into a struggle for global dominance, known as the Cold War, with the rivalling United States and NATO.
After Stalin's death in 1953 and a short period of collective leadership, the new leader Nikita Khrushchev denounced Stalin and launched the policy of de-Stalinization, releasing many political prisoners from the Gulag labour camps. The general easement of repressive policies became known later as the Khrushchev Thaw. At the same time, Cold War tensions reached its peak when the two rivals clashed over the deployment of the United States Jupiter missiles in Turkey and Soviet missiles in Cuba.
In 1957, the Soviet Union launched the world's first artificial satellite, Sputnik 1, thus starting the Space Age. Russian cosmonaut Yuri Gagarin became the first human to orbit the Earth, aboard the Vostok 1 crewed spacecraft on 12 April 1961.
Following the ousting of Khrushchev in 1964, another period of collective leadership ensued, until Leonid Brezhnev became the leader. The era of the 1970s and the early 1980s was later designated as the Era of Stagnation. The 1965 Kosygin reform aimed for partial decentralisation of the Soviet economy. In 1979, after a communist-led revolution in Afghanistan, Soviet forces invaded the country, ultimately starting the Soviet–Afghan War. In May 1988, the Soviets started to withdraw from Afghanistan, due to international opposition, persistent anti-Soviet guerrilla warfare, and a lack of support by Soviet citizens.
From 1985 onwards, the last Soviet leader Mikhail Gorbachev, who sought to enact liberal reforms in the Soviet system, introduced the policies of glasnost (openness) and perestroika (restructuring) in an attempt to end the period of economic stagnation and to democratise the government. This, however, led to the rise of strong nationalist and separatist movements across the country. Prior to 1991, the Soviet economy was the world's second-largest, but during its final years, it went into a crisis.
By 1991, economic and political turmoil began to boil over as the Baltic states chose to secede from the Soviet Union. On 17 March, a referendum was held, in which the vast majority of participating citizens voted in favour of changing the Soviet Union into a renewed federation. In June 1991, Boris Yeltsin became the first directly elected President in Russian history when he was elected President of the Russian SFSR. In August 1991, a coup d'état attempt by members of Gorbachev's government, directed against Gorbachev and aimed at preserving the Soviet Union, instead led to the end of the Communist Party of the Soviet Union. On 25 December 1991, following the dissolution of the Soviet Union, along with contemporary Russia, fourteen other post-Soviet states emerged.
