Freikorps (English: Free Corps) are German volunteer military or paramilitary units. The term was originally applied to voluntary armies formed in German lands from the middle of the 18th century onwards. Between World War I and World War II the term was also used for the paramilitary organizations that arose during the period of the Weimar Germany. Freikorps units fought both for and against the German state. They formed the vanguard of the Nazi movement.