The primary ideology of the Soviet Union after the Russian Revolution was Marxism-Leninism. This ideology blended the principles of Karl Marx’s theories of class struggle and communism with the ideas formulated by Vladimir Lenin, who emphasized the role of a vanguard party to lead the proletariat to revolution. Marxism-Leninism justified the establishment of a one-party state, asserting that a transitional socialist phase was essential before achieving a classless, stateless communist society. It became the guiding doctrine for Soviet policies and shaped the USSR's domestic and foreign strategies throughout its existence.