Originally, the Freikorps were voluntary armies organized in the German states and principalities in the middle of the 18th century. They were recruited by Frederick II of Prussia to keep law and order when the regular soldiers were busy fighting in the Seven Years War.
The original Freikorps did not constitute professional regular armies, and they were formed in periods of emergency for secondary duties to keep order in time of war. Early in the 19th century, Freikorps were organized to fight against the French invaders that plundered the German villages and farms during the Napoleonic Wars. “Freikorps” is a German word which means “Free Corps” in English.
At the end of World War I, new Freikorps organizations were created by army officers and soldiers, who had fought in the Great War, to put down the riots during the German Revolution of 1918. They volunteered to join these patriotic paramilitary armies to fight against armed communist activists who attempted to seize power in Germany and set up a Marxist regime, similar to the one that had been established in Russia in 1917. German communists and anarchists were organized around the Marxist Spartacist League.
With the support from Minister of Defense Gustav Noske, a member of the Social Democratic Party of Germany, of the Weimer Republic, the Freikorps managed to quell the communist uprisings. In May 1919, this German militia army overthrew the illegal Soviet-backed government of Bavaria, which had been established by force by the communists. Later, many Freikorps members, such as Ernst Röhm, Reynhard Heydrich, Adolf Hitler, and Wilhelm Keitel, would join the German Workers Party, which was later renamed the National Socialist German Workers Party, NSDAP, Nazi.