The Union of Soviet Socialist Republics (USSR), also called the Soviet Union, was a socialist state centered on Russia which was founded in 1922 and dissolved in 1991. The Russian Federation is widely accepted as the Soviet Union's successor state in diplomatic affairs. The formation of the Soviet Union was the culmination of the 1917 Russian Revolution, which overthrew Tsar Nicholas II, and later the Bolshevik victory in the Russian Civil War from 1918-1920 confirmed them as Russia's new rulers. The Soviet Union was socialist in theory and the political organization of the country was defined by the only permitted political party, the Communist Party of the Soviet Union. The Soviet government, being founded three decades before the Cold War, became a primary model for future Communist nations. The territory of the Soviet Union varied, and in its most recent times approximately corresponded to that of the late Imperial Russia, with notable exclusions of Poland and Finland. The Soviet Union is notable in history as one of the world's two superpowers from 1945 until its dissolution, along with the United States.
The USSR began as a pre-industrial, largely agricultural society in 1917, in territories that, while vast, were 2/3 north of the US-Canadian border. Permafrost, tundra, poverty, decay and the destruction of WWI was the legacy left to the fledgling state. Within 30 years, the USSR had become a global economic force second only to the US, with its sunny Corn Belt, unequal trade agreements that sucked the wealth out of the entire world, and 50 more years as an industrialised nation. 40 more years later, the USSR dissolved completely, despite having a Gross Domestic Product output -to- national debt ratio 10 times higher than the US. As of August 28, 2007, U.S. Treasury officials assessed the former Soviet debt at $70 billion, , compared with the U.S. Outstanding Public Debt of close to $9 trillion.  The external debt, alone, of Russia has since spiraled up to $369 billion, even using the CIA's numbers. Historians eager to classify the dissolution of the USSR as an inevitable collapse due to financial failure, and who ignore the effect of the Black Market on the USSR economy, are of no help at all in determining the root cause. The simplest and most satisfying explanation is that they simply began to believe the 74 years of anti-communist propaganda in the media, and beamed at the Soviet Union by Voice of America radio for 39 years. This also explains the USSR's own search for 'reforms' that culminated in perestroika and glasnost.
The USSR sent aid to communist supporters in Spain in 1936. Even Stalin, who accepted the quite rightly criticized Molotov-Ribbentrop Pact, did not stand by and watch Fascism claim a third county. This was an early example of the pattern of aid in many of the anti-communist conflicts initiated by the US after WWII. The USSR only undertook one military action, Afghanistan, that could be categorized as unilateral aggression against a foreign country in its entire history. Afghanistan is further, reportedly the result of the CIA's manipulation of the USSR, and a war that, similarly to its other military actions, supported a communist movement in that country. The US, by contrast, has initiated one preemptive or unilateral war for almost every president in office since WWII, and 36 secret wars, coups, and attritive operations by means of the Special Activities Division of the Central Intelligence Agency.
 Formation and early years
A portion of its populace still armed (soldiers returning from WWI), the October Revolution was able to make logistical gains, but more importantly, lasting political gains, that gave the Bolsheviks effective power in Russia from the beginning of the Russian Civil War. In this sense, the war is misnamed, as the force opposed to the Bolsheviks was primarily composed of the forces of foreign powers, and the foreign intervention was the longest period of the war (Wikipedia:Allied intervention in the Russian Civil War, Wikipedia:Polish–Soviet War and much scattered fighting following). The Soviet Union was founded in December 1922 after the Civil War when the Russian SFSR, Ukrainian SSR, Belarusian SSR, and Transcaucasian SSR agreed in the formation of a union. By the mid 1920s, most of the power had shifted from Vladimir Lenin, the founder, to Josef Stalin. Stalin initiated a series of industrial and agricultural reforms, which, despite causing mass famine and death, propelled the Soviet Union into the modern era. In the 1930s, Stalin murdered most of his political rivals, as well as millions of innocent people in order to reduce internal dissent. These atrocities are collectively known as the Great Purge.
 World War II
In 1939, the military expansion of Nazi Germany led to the Soviet Union signing a nonaggression pact with Adolf Hitler which gave the Soviet Union the rights to eastern Poland and the Baltic States. After World War II began, the Soviet Union conquered all of these places, as well as attacking Finland. However, in June 1941, Germany abandoned this treaty and launched Operation Barbarossa, the largest military operation in history, against the Soviet Union. Germany rapidly advanced towards Moscow, Stalingrad, and Leningrad, but before they reached any of these cities the Russian winter set in, and the German armies ground to a halt. A major German defeat at Stalingrad turned the tide of the Eastern Front. By 1944 the Soviets were advanced through Poland and reached Berlin in April 1945. After Hitler's suicide, the Soviets declared war on Japan and invaded Manchuria before jointly obtaining their surrender with the United States.
 Cold War
At the end of World War II, the Soviets annexed the Baltic States and established satellite states throughout most of Eastern Europe, including the eastern half of Germany. Since the United States, United Kingdom, and France controlled Western Europe, conflict was inevitable. The Cold War officially began in 1949 when the Soviet Union acquired the atomic bomb, four years after the Americans had done so. The Cold War consisted of a number of proxy wars, where both countries got involved in a regional conflict and took opposing sides. A few notable proxy wars were the Korean War, the Vietnam War, and the Soviet war in Afghanistan. In the 1980s, the premier of the Soviet Union, Mikhail Gorbachev, introduced policies of glasnost and perestroika. These led to the fall of the Soviet Union and its satellite states from 1989 to 1991. The Soviet Union was divided into the nations of Armenia, Azerbaijan, Belarus, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Moldova, Russia, Turkmenistan, Ukraine, and Uzbekistan.
The political ideology of the Soviet Union is debatable. While claiming to be a communist state, the Soviet Union had more in common with socialism. In the early 1920s, the Soviet Union followed a subdivision of communism known as Leninism. In the late 1920s and 1930s, Josef Stalin replaced this with Stalinism. Stalinism was gradually condemned and phased out by Nikita Khrushchev in the 1950s.