During war, civilians have been concentrated in camps to prevent them from engaging in guerrilla warfare or from providing aid to enemy forces, or simply as a means of terrorizing the populace into submission. During the South African War (1899-1902) the British confined noncombatants of the republics of Transvaal and Cape Colony in concentration camps. Another instance of interning noncombatant civilians occurred shortly after the outbreak of hostilities between Japan and the United States (Dec. 7, 1941), when more than 100,000 Japanese and Japanese-Americans on the West Coast were taken into custody and placed in camps in the interior.

Political concentration camps instituted primarily to reinforce the state's control have been established in various forms under many totalitarian regimes--most extensively in Nazi Germany and the Soviet Union. To a considerable extent, the camps served as the special prisons of the secret police. Nazi concentration camps were under the administration of the SS; forced-labour camps of the Soviet Union were operated by a succession of organizations beginning in 1917 with the Cheka and ending in the early 1990s with the KGB.

The first German concentration camps were established in 1933 for the confinement of opponents of the Nazi Party--Communists and Social Democrats. Political opposition soon was enlarged to include minority groups, chiefly Jews, but by the end of World War II many gypsies, homosexuals, and anti-Nazi civilians from the occupied territories had also been liquidated. After the outbreak of World War II the camp inmates were used as a supplementary labour supply, and such camps mushroomed throughout Europe. Inmates were required to work for their wages in food; those unable to work usually died of starvation, and those who did not starve often died of overwork. The most shocking extension of this system was the establishment after 1940 of extermination centres, or "death camps." They were located primarily in Poland, which Adolf Hitler had selected as the setting for his "final solution" to the "Jewish problem." The most notorious were Auschwitz, Majdanek, and Treblinka. (See extermination camp.) At some camps, notably Buchenwald, medical experimentation was conducted. New toxins and antitoxins were tried out, new surgical techniques devised, and studies made of the effects of artificially induced diseases, all by experimenting on living human beings.

In the Soviet Union by 1922 there were 23 concentration camps for the incarceration of persons accused of political offenses as as well as criminal offenses. Many corrective labour camps were established in northern Russia and Siberia, especially during the First Five-Year Plan, 1928-32, when millions of rich peasants were driven from their farms under the collectivization program. The Stalinist purges of 1936-38 brought additional millions into the camps--said to be essentially institutions of slavery.

The Soviet occupation of eastern Poland in 1939 and the absorption of the Baltic states in 1940 led to the incarceration of large numbers of non-Soviet citizens. Following the outbreak of war with Germany in 1941, the camps received Axis prisoners of war and Soviet nationals accused of collaboration with the enemy. After the death of Joseph Stalin in 1953, many prisoners were released and the number of camps was drastically reduced. See also Gulag.