Rossiĭskai︠a︡ sot︠s︡ial-demokraticheskai︠a︡ rabochai︠a︡ partii︠a︡

The Bolsheviks (Russian: большевики, bol'sheviki; from большинство, bol'shinstvo, 'majority'), led by Vladimir Lenin, were a radical faction of the Marxist Russian Social Democratic Labour Party (RSDLP) which split with the Mensheviks at the Second Party Congress in 1903. The Bolshevik party, formally established in 1912, seized power in Russia in the October Revolution of 1917, and was later renamed the Russian Communist Party, All-Union Communist Party, and ultimately the Communist Party of the Soviet Union. Its ideology, based on Leninist and later Marxist–Leninist principles, became known as Bolshevism. The origin of the RSDLP split was Lenin's support for a smaller party of professional revolutionaries, as opposed to the Menshevik desire for a broad party membership. The influence of the factions fluctuated in the years up to 1912, when the RSDLP formally split in two. The political philosophy of the Bolsheviks was based on the Leninist principles of vanguardism and democratic centralism. Lenin was also more willing to use illegal means such as robbery to fund the party's activities. Influenced by the experience of World War I, by 1917 he had concluded that the chain of world capitalism could "break at its weakest link" in Russia before it had reached the level of the advanced countries, contrary to theorists such as Georgi Plekhanov. Lenin had also come to view poorer peasants as potential allies of the relatively small Russian proletariat. After the February Revolution of 1917, Lenin returned to Russia and issued his April Theses, which called for "no support for the Provisional Government" and "all power to the soviets". During the summer of 1917, which saw events including the July Days and Kornilov affair, large numbers of radicalized workers joined the Bolsheviks, which planned the October Revolution that overthrew the government. The Bolsheviks initially governed in coalition with the Left Socialist-Revolutionaries, but increasingly centralized power and suppressed opposition during the Russian Civil War, and after 1921 became the sole legal party in Soviet Russia and the Soviet Union. Under Joseph Stalin's leadership, Bolshevism became linked to his policies of "socialism in one country", rapid industrialization, collectivized agriculture, and centralized state control.