The October Revolution of Russia in 1917 was a major turning point in Russian, and indeed world history when Vladimir Lenin, Leon Trotsky and the rest of the Bolshevik Party marched through Petrograd and took power from the Provisional Government which had ruled Russia since the February Revolution of the same year. The Bolsheviks established the first Marxist Communist state in the world.
Russia and her Empire had been ruled since the beginning of March of the same year by a Provisional Government which had replaced the Tsarist regime in the February Revolution of the same year. The government's failings to successfully address the needs of Russia ultimately lead to its downfall at the hands of the Bolsheviks. how much can a new government do in just a few months? The main grievance of the Russian people with the Provisional Government was its failure to withdraw from World War One, despite pledging to when it first gained power.
The revolution itself succeeded when the Russian Red Guard successfully took control of the Winter Palace on the night of October 25th, where I'm assuming the Russian Provisional Government guys were hanging out.
Lenin took over Russia, kicked capitalists in for three years in the Russian Civil War, and went about creating the Soviet Union. Unfortunately, Lenin died, and Stalin took power, who went about killing millions and millions of his own countrymen in the 1930s.