The USSR – officially called the Union of Soviet Socialist Republics (see ABBREVIATIONFINDER) – was a Marxist-Leninist federal state that existed in Eurasia between 1922 and 1991.
The USSR was born as a union of four Soviet socialist republics, formed after the October Revolution of 1917, and grew to 15 by 1956.
The geographical boundaries of the Soviet Union varied over time, but after World War II, from 1945 to dissolution, the boundaries roughly corresponded to those of the defunct Imperial Russia, with the notable exclusions of Poland, most of Finland, and Alaska.
It was often improperly referred to as Russia, as its largest and most dominant constituent state. From 1945 to 1991, in the period known as the Cold War, the Soviet Union and the United States were the two world superpowers that dominated the global agenda of economic policy, foreign affairs, military operations, cultural exchange, scientific progress including the initiation of space exploration, and sports (including the Olympics).
Over and above the errors that led to its disappearance, this country played an essential role in the defeat of fascism and in the advancement of humanity towards new forms of more just and supportive social organization.
The Soviet Union was established in December 1922 as the Union of Soviet Republics of Russia (known as Bolshevik Russia), Ukraine, Belarusand Transcaucasia governed, the first three, by Bolshevik parties and the last by the Menshevik.
The Revolution and the founding of the Soviet state
First flag of the Soviet Union, it was created in 1923 and remained until 1953
The Great October Revolution was one of the most relevant and momentous events of the 20th century, it was a true revolution that shook the world, where the great leading role of Lenin and his Marxist conception that gave rise to the Bolshevik Party stood out.
Vladimir Ilyich Ulyanov Lenin
The popular uprising in Petrograd culminated in the overthrow of the imperial government in March 1917.
To ensure the rights of the working class, workers’ assemblies, known as Soviets, are born throughout the country. The Bolsheviks, led by Vladimir Ilyich Lenin, pressed for a socialist revolution both in these assemblies and in the streets, overthrowing the Provisional Government on November 7, October 25 according to the Julian Calendar, 1917 and handing over power to the soviets of workers, soldiers and peasants.
Only after the long and bloody Russian Civil War of 1918 – 1921, during which the first Soviet Constitution of 1918 was passed, did the new Soviet power take hold.
Unification of the Soviet republics
On December 29, 1922, a conference of plenipotentiary delegations from Russia, Transcaucasia, Ukraine and Belarus approved the Treaty of Creation of the USSR and the Declaration of the Creation of the USSR, forming the Union of Soviet Socialist Republics.
These two documents were confirmed by the first Soviet Congress of the USSR and signed by the heads of the delegations Mikhail Kalinin, Mikha Tskhakaya, Mikhail Frunze and Grigory Petrovsky, and Aleksandr Chervyakov respectively on December 30, 1922. On February 1, 1924 the USSR was recognized by the first world power of the time, the British Empire.
Lenin’s untimely death in January 1924 triggered a fierce power struggle. The main antagonists were Trotsky and Iósif Stalin, then general secretary of the party, who proclaimed themselves legitimate heirs of Lenin. Thanks to control over the party apparatus, Stalin managed to win the support of the majority of its members and thus consolidate his power. In November 1927, after an internal referendum, the party completely repudiated the political ideas of Trotsky, who was expelled from it and had to go into exile in Alma Ata (present-day Almaty, in Kazakhstan). Two years later, Trotsky was exiled from the USSR. There were rumors of a secret alliance between Trotsky and the German and Japanese governments offering them some Soviet territories to help him assume power in the rest of Russia. It is possible that it was the fascists who spread these rumors.  In 1940 he was assassinated in Mexico at the hands of a Soviet agent.
In 1929, Stalin was recognized as the top leader of the party and the state. From that moment he began the series of purges that would characterize his years in office, and which affected his former allies in the first place during the struggle with Trotsky. These leaders, especially Nikolai Ivanovich Bukharin and Alexey Ivanovich Rykov, were expelled from the highest organs of the party.
In foreign policy the Molotov-Ribbentrop Pact: The 23 of August of 1939, the Soviet Union and Germany signed in Moscow a pact of non – aggression, which also in a secret additional protocol that is territorial and political reorganization of the areas belonging to the Polish state, the Soviet and German spheres of influence are limited approximately to the line of the Narev, Vistula and San rivers.  The NSDAP he prepared to negotiate on western Ukraine with the Polish government but not with the Soviets. Western Ukraine is situated integrally within the Soviet sphere of influence as the protocol defined it. General Franz Halder wrote in his posts that the fascists discussed the formation of an independent state in western Ukraine. The Soviets would anticipate a negotiated settlement that would leave a remnant Polish state between Germany and the Soviet boundary. Most of western Poland would have continued as part of reduced Poland. 
“I think that the imperialist plans to launch Hitler against the USSR would never have justified Hitler’s pact with Stalin, it was very harsh. The communist parties, which were characterized by discipline, were all forced to defend the Molotov-Ribbentrop Pact already bleed out politically. ”