World War I demonstrated tsarist corruption and inefficiency and only patriotism held the poorly equipped army together for a time. Disorders broke out in Petrograd (renamed Leningrad and now St. Petersburg) in March 1917, and defection of the Petrograd garrison launched the revolution. Nicholas II was forced to abdicate on March 15, 1917, and he and his family were killed by revolutionists on July 16, 1918. A provisional government under the successive premierships of Prince Lvov and a moderate, Alexander Kerensky, lost ground to the radical, or Bolshevik, wing of the Socialist Democratic Labor Party. On Nov. 7, 1917, the Bolshevik revolution, engineered by N. Lenin (Lenin was the pseudonym taken by Vladimir Ilich Ulyanov) and Leon Trotsky, overthrew the Kerensky government and authority was vested in a Council of People's Commissars, with Lenin as premier. The series of events leading to the revolution was from now on as October Revolution, since Nov 7 was actually Oct 25 under the Old Russian Calendar.
The humiliating Treaty of Brest-Litovsk (March 3, 1918) concluded the war with Germany, but a brutal civil war and foreign intervention delayed Communist control of all Russia until 1920. A brief war with Poland in 1920 resulted in Russian defeat.