The Marxism of the Third International (1819–circa 1945) and "Marxism-Leninism" (from 1924)

This period saw consequential divisions within the labour movement. Unlike earlier periods, these divisions were not so much due to open arguments on the "correct" interpretation, further development or political implementation of Marxist critique. Nor was the focus on questions of theory and critique, as was the case in Western and heterodox Marxism, and later in the post-1960 re-engagement with Marx (though such questions were for instance pursued by the Soviet psychologist Aleksei Nikolaevich Leontiev, and by Isaak Illich Rubin; Rubin fell victim to Stalinist terror in 1937). Rather, most of this period's conflicts were closely linked to factional disputes over political questions, and to power struggles. This can be seen from texts associated with opposing currents within the German Communist Party, such as those of Heinrich Brandler and August Thalheimer.

Within the sphere of influence of the Soviet communists associated with the Bolshevik Party, a dogmatic "Marxism-Leninism" asserted itself; it was declared state doctrine first in the Soviet Union and later in other socialist countries. By contrast, and in continuation of earlier discussions, there emerged the more social-democratic oriented Austro-Marxism, left socialism, which was rather libertarian-communist in orientation, and left communism.