Since early 1917, Russia had been in a state of turmoil. Two revolutions took place in 1917. The first overthrew the imperial govenment. The second brought the Bolsheviks to power. These events are referred to collectively as the Russian Revolution.
In February 1917, the Czarist government's poor management of World War I had helped to inspire a popular uprising, known as the February Revolution. This revolution forced the abdication of Czar Nicholas II and placed in power a Provisional Government of liberal and socialist factions, ultimately under the leadership of Socialist Revolutionary party member Alexander Kerensky. This brief experiment with pluralist democracy was a chaotic one, and in the summer months, the continual deterioration of the war effort and an increasingly dire economic situation caused Russian workers, soldiers, and sailors to riot ("The July Days").
On October 24–25, 1917, Bolshevik (left-wing socialist) forces under Vladimir Lenin seized key government buildings and stormed the Winter Palace, then the seat of the new government in Russia's capital, Petrograd (now St. Petersburg). The "Great October Socialist Revolution," the first successful Marxist coup in history, dislodged the ineffectual Provisional Government, and ultimately established a Soviet Socialist Republic under Lenin's leadership.
The new Soviet state's radical social, political, economic, and agrarian reforms would in the postwar years unnerve western democratic governments, who so feared the spread of Communism throughout Europe that they were willing to compromise or appease right-wing regimes (including Adolf Hitler's Nazi Germany) in the 1920s and 1930s.