She cofounded what became the Polish Communist Party (1893), before obtaining German citizenship in 1898. Imprisoned in 1915 for opposing World War I, she cofounded the revolutionary and pacifist group known as the Spartacus League (the Spartacists) in 1916 with the German socialist Karl Liebknecht (1871–1919). After her release from prison in 1918 she cofounded the German Communist Party; the following year she and Liebknecht were assassinated after organizing an abortive Communist uprising in Berlin.