As a result of the Soviet invasion of Poland in 1939, hundreds of thousands of Polish soldiers became prisoners of war in the Soviet Union. Thousands of them were executed; over 20,000 Polish military personnel and civilians perished in the Katyn massacre. Out of Anders’ 80,000 evacuees from Soviet Union gathered in Great Britain only 310 volunteered to return to Poland in 1947.
According to some sources, the Soviets captured 3.5 million Axis servicemen (excluding Japanese) of which more than a million died. According to G. Krivosheev, the Soviets captured in total 4,126,964 Axis servicemen, of which 580,548 died in captivity. Of 2,389,560 German servicemen 450,600 died in captivity. One specific example of the tragic fate of the German POWs was after the Battle of Stalingrad, during which the Soviets captured 91,000 German troops, many already starved and ill, of whom only 5,000 survived the war. The last German POWs (those who were sentenced for war crimes, sometimes without sufficient reasons) were released by the Soviets in 1955, only after Joseph Stalin had died. At least 54,000 Italian POWs died in Russia, with a mortality rate of 84.5%. See also POW labor in the Soviet Union, Japanese prisoners of war in the Soviet Union, Italian prisoners of war in the Soviet Union, Romanian POW in the Soviet Union.
During the war the Armies of Allied nations such as the U.S., UK, Australia and Canada were ordered to treat Axis prisoners strictly in accordance with the Geneva Convention (1929). Some breaches of the Convention took place, however. According to Stephen E. Ambrose, of the roughly 1,000 U.S. combat veterans that he had interviewed, roughly 1/3 told him they had seen U.S. troops kill German prisoners.
Although some Japanese were taken prisoner, most fought until they were killed or committed suicide. Of the 22,000 Japanese soldiers present at the beginning of the Battle of Iwo Jima, over 20,000 were killed and only 1,083 taken prisoner. Of the 30,000 Japanese troops that defended Saipan, less than 1,000 remained alive at battle’s end. Japanese prisoners sent to camps in the U.S. fared well but many Japanese were killed when trying to surrender or were massacred just after they had surrendered. Some Japanese prisoners in POW camps died at their own hands, either directly or by attacking guards with the intention of forcing the guards to kill them.
Towards the end of the war in Europe, as large numbers of Axis soldiers surrendered, the U.S. created the designation of Disarmed Enemy Forces (DEF) so as not to treat prisoners as POWs. A lot of these soldiers were kept in open fields in various Rheinwiesenlagers. Controversy has arisen about how Eisenhower managed these prisoners. Many died when forced to clear minefields in Norway, France etc. How many died during the several post-war years that they were used for forced labor in France, the Soviet Union, etc, is disputed. The “London Cage”, a MI19 prisoner of war facility in the UK during and immediately after WWII, was subject to frequent allegations of torture.