Japanese prisoner-of-war camps, many of which were used as labour camps, also had high death rates. The International Military Tribunal for the Far East found the death rate of Western prisoners was 27.1 per cent , seven times that of POWs under the Germans and Italians. While 37,583 prisoners from the UK, 28,500 from the Netherlands, and 14,473 from the United States were released after the surrender of Japan, the number of Chinese released was only 56. At least five million Chinese civilians from northern China and Manchukuo were enslaved between 1935 and 1941 by the East Asia Development Board, or Kōain, for work in mines and war industries. After 1942, the number reached 10 million. In Java, between 4 and 10 million rōmusha , were forced to work by the Japanese military. About 270,000 of these Javanese labourers were sent to other Japanese-held areas in South East Asia, and only 52,000 were repatriated to Java.
Question: How many countries had people prisoned by Japan?
Answer: 4