Bolshevism, Communist doctrine based on the theories of Karl Marx as formulated by Vladimir Ilich Lenin. These theories were outlined at the second congress of the Russian Social Democratic Labour party held in London in 1903. The divergent viewpoints of the delegates to the congress crystallized into two factions, the more radical faction being led by Lenin. He advocated a unified party of active, professional revolutionary members, willing to use any means to establish a Communist society. His opponents, on the other hand, proposed to admit all who declared general sympathy with the aims of the party, regardless of active participation. On this point the congress supported the latter plan, but on other matters and in the final vote that elected the party leadership, the congress favoured Lenin. The faction led by Lenin was thereupon called Bolshevik (from the Russian word for "majority"), and the opposition, Menshevik (from the Russian word for "minority"). The names clung, although the Bolsheviks were not always thereafter the dominant group in the Russian revolutionary movement.