The October Revolution of 1917 is one of the key events of Russian history. It completes the chapter of the Russian Empire and the Romanov royal family as the ruling dynasty, and thus begins the history of Soviet Russia and the USSR. Prior to the Revolution of 1917, very significant was revolution in 1905, which forced the emperor to make concessions in the sense of greater rights for minorities, summoning Duma, democratizing the society, and weakening emperor powers. The social cohesion and the state of the country that improved after the 1905 events, will be disrupted by the war, that is, the First World War, in which the Russian Empire will be included on the side of Triple Entente. The Russian Empire will lose a large number of people in the war, which will be one of the triggering factors for the new revolution. Poverty and hunger will encourage citizens of Petrograd to protest, and that, will turn into the February Revolution, after which the emperor will abdicate, and the Provisional Government will be formed under the leadership of the Liberal Democratic Party. The government's inability and persistence of left-wing currents to stop the country from participating in the war and carry out major reforms, will lead to new rebellions. Under the leadership of Vladimir Lenin and Leon Trotsky, the October Revolution will begin, and it will abolish the Provisional Government and create a new state government under the leadership of the Bolsheviks. Ultimately, the Union of Soviet Socialist Republics will be formed, a country that will play the role of the world superpower throughout the 20th century.