On August 4, 1914, in the Reichstag—the imperial German parliament—the SPD (Socialist Party of Germany) deputies voted overwhelmingly in favour of the Second Reich's war effort. This decision sparked an internal split within the party, between those who chose to abandon their ideology to safeguard their homeland and those who remained faithful to internationalist principles. The latter began to be persecuted by the imperial regime and imprisoned, as in the cases of Rosa Luxembourg and Karl Liebknecht, leaving their ideals in the hands of several clandestine organisations, the most famous of which was the Spartacus League.

The Spartacus League was a decentralised, illegal organisation without an official structure throughout the First World War, and its propaganda efforts are attributed to the continued work and dedication of Lithuanian exile Leo Jogiches. The latter pulled the organisation's strings through constant leaflet distribution, which reached its peak during the Berlin workers' uprisings in January 1918, with a circulation of up to 100,000 copies per leaflet.

The League's importance reached its peak with the communist uprising in Berlin on November 9, 1918. This was initially successful with the Kaiser's abdication and the occupation of public buildings, administrative offices, newspaper offices, and strategic locations by workers and revolutionaries. Communist leader Liebknecht was invited to seek a compromise with the SPD to form a government, an option opposed by all of the SPD's allies and therefore rejected. The revolution, carried out largely thanks to the Spartacus League, ultimately failed to deliver results.

This episode would only be the beginning of the isolation of the communist group that had centred on the Spartacus League. It later transformed into the more organised KPD—the German Communist Party—and was opposed by the socialist-led government in any revolutionary effort, most of which were conceived by Luxembourg. The epic of German communist revolutionary hopes officially ended on January 15, 1919. On that day, the two leading communist figures, Liebknecht and Luxembourg, after taking refuge in the homes of comrades, were found by the Freikorps—German war veterans enrolled in paramilitary organisations designed to maintain public order—hired by the socialist SPD government and murdered without trial.