The Third International, also known as the Communist International (Comintern), was established as a result of the victory of the 1917 October Revolution in Russia. Its purpose was to assemble revolutionary movements worldwide that could work together to "hasten the victory" of international socialism and the dismantling of capitalism. It was created as a response to the failure of the Second International, which broke up by 1916 over the issue of World War I, with the revolutionary wing opposing it and the reformists supporting it.

The first congress of the Comintern was held in Moscow March 2-6 1919, whilst the Russian Civil War was ongoing. Thirty-five organisations from over twenty countries were represented at this founding congress, despite many logistical difficulties.

The second congress of the Comintern occurred in July 1920, and over 60 organisations were represented from 40 countries, including many from outside Europe. Here, the twenty-one conditions on being admitted to the Third International were established, and a solution was sought on how to reach the international proletariat who sympathised with the Russian Revolution but still followed centrist leaders. Historian E. H. Carr described this congress as "the crowning moment in the history of the Comintern as an international force, the moment when the Russian revolution seemed most certainly on the point of transforming itself into a European revolution."

The Comintern continued to hold meetings until it was formally dissolved in 1943.