During World War II millions of prisoners of war were killed or died while in foreign custody. German, Russian, and Japanese treatment of POWs was particularly brutal. After the war international tribunals punished this treatment of POWs as war crimes. The Geneva Convention of 1949 broadened the definition of prisoner of war to include civilians.

During the Korean War (1950-53), United Nations forces accused the Chinese and the North Koreans of brainwashing their POWs. The North and South Vietnamese governments were also charged with violating the Geneva Convention during the Vietnam War. The Pentagon declared the last official POW dead in 1994, but its MIA (missing in action) list still has names of missing US servicemen.

Before the 17th century, war prisoners were traditionally killed or enslaved. The Treaty of Westphalia (1648), ending the Thirty Years' War, is seen by many historians as the turning point in the recognition of the status of prisoner of war. Under the terms of the treaty, prisoners were released without ransom. During the American Civil War (1861-65), German-born US political reformer Francis Lieber drafted the first set of regulations concerning prisoners of war, which was later used as a basis for the Hague Convention.

As a result of the war on terror, the classification of POWs has recently come into question. The USA has termed many detainees from Afghanistan as enemy combatants and has not afforded them the rights available under the Geneva Convention.