In the midst of the Great War, and partly as a result of Russian policy in the conflict, the residents of Petrograd (St. Petersburg) engaged in a spontaneous rebellion that eventually toppled the tsar in February/March 1917. After this February Revolution, continued war weariness, combined with questions over Russia's role in the conflict and the weakness of the Provisional Government, led to another Revolution. In October 1917, Vladimir Lenin and his Bolshevik Party, one of the most radical Marxist parties in the country, seized power. This October Revolution took Russia out of the Great War, but led to Civil War over the next two years. In addition, Lenin and his Party (later renamed the Communist Party) attempted to build the world's first socialist society based on Marxist principles and renamed this entity the Union of Soviet Socialist Republics. When Lenin died in 1924, his heirs engaged in a bitter struggle over how to carry on this task. Eventually, Joseph Stalin, a Georgian revolutionary who had served in Lenin's first cabinet and later built a power base from his position of General Secretary, became the undisputed leader of the Soviet Union. In 1929, Stalin launched a "revolution from above," one designed to industrialize the country as quickly as possible, collectivize agriculture, and bring a "Cultural Revolution" to the Soviet people. In addition, in the mid-1930s, Stalin carried out a series of purges that cleansed the Party of many of its long-standing members, plunging Soviet society into what has been termed the Great Terror. When the purges ended in 1939, millions had been killed or imprisoned, and Stalin's control over the Party and Lenin's legacy seemed absolute.