The Spartacus League was a Marxist revolutionary movement organized in Germany during World War I. It was founded in August 1914 as the International Group by Rosa Luxemburg, Karl Liebknecht, Clara Zetkin, and other members of the Social Democratic Party of Germany (SPD) who were dissatisfied with the party's official policies in support of the war. In 1916 it renamed itself the Spartacus Group and in 1917 joined the Independent Social Democratic Party of Germany (USPD), which had split off from the SPD as its left wing faction.

Rosa Luxemburg was a Polish and naturalised-German revolutionary socialist, orthodox Marxist, and anti-War activist during the First World War. She became a key figure of the revolutionary socialist movements of Poland and Germany during the late 19th and early 20th century, particularly the Spartacist uprising.