Clara Zetkin (nee Eissner; 5 July 1857  20 June 1933) was a German Marxist theorist, activist, and advocate for women's rights. In 1911, she organized the first International Women's Day. Until 1917, she was active in the Social Democratic Party of Germany, then she joined the Independent Social Democratic Party of Germany (USPD) and its far-left wing, the Spartacist League; this later became the Communist Party of Germany (KPD), which she represented in the Reichstag during the Weimar Republic from 1920 to 1933. Rosa Luxemburg (also Rozalia Luxenburg; Polish: R??a Luksemburg; 5 March 1871  15 January 1919) was a Marxist theorist, philosopher, economist and revolutionary socialist of Polish-Jewish descent who became a naturalized German citizen. She was, successively, a member of the Social Democracy of the Kingdom of Poland and Lithuania (SDKPiL), the Social Democratic Party of Germany (SPD), the Independent Social Democratic Party (USPD), and the Communist Party of Germany (KPD).