The Russian Revolution tore the socialist community in two. Many European socialists doubted whether the Bolshevik revolution was really socialist. Lenin declared that democratic socialists were traitors and renegades. In January 1918, the Bolshevik party formally acknowledged the break between social democrats and communists by changing its name from the Russian Social-Democratic Labor Party (Bolshevik) to the Russian Communist Party.

In 1919, Lenin pre-empted efforts by moderate socialist leaders to revive the Second International, by creating his own international organization. In May 1919, Russia hosted the first meeting of the Communist International, also known as the Comintern, in Moscow. Unlike the First and Second International, the Comintern accepted no variations in socialist philosophy. The organization's stated purpose was to promote the spread of the socialist revolution across the industrialized world. In order to be admitted to the Comintern, socialist parties were required to model themselves on the Bolshevik party pattern and expel moderate socialists and pacifists from their membership rolls.