Definitions of Japanese war crimes

Although the 1929 Geneva Convention on Prisoners of War provided the regulations how prisoners of war should be treated, the Empire of Japan never signed the agreement (except the 1929 Geneva Convention on the Sick and Wounded).[2] However, many of the alleged crimes committed by imperial personnel were also violations of the Japanese code of military law, which Japanese authorities either ignored or failed to enforce. The empire also violated provisions of the Treaty of Versailles, such as article 171, which outlawed the use of poison gas (chemical weapons), and other international agreements signed by Japan, such as the Hague Conventions of 1899 and 1907, which protect prisoners of war (POWs). According to historian Akira Fujiwara, Hirohito personally ratified on 5 August 1937 a proposition by his Army chief of staff, Prince Kan'in , to remove the constraint of those conventions on the treatment of Chinese prisoners.[3]

Outside Japan, different societies use widely different timeframes in defining Japanese war crimes. For example, the annexation of Korea by Japan in 1910 was followed by the abolition of the traditional class system by Joseon and modernization against the Korean people. Thus, some Koreans refer to "Japanese war crimes" as events occurring during the period shortly prior to 1910 to 1945. Events such as the March 1st movement where 7,000 people were killed[4] and the murder of Empress Myeongseong are considered war crimes in Korea. By comparison, the United States did not come into military conflict with Japan until 1941, and thus Americans may consider "Japanese war crimes" as encompassing only those events that occurred from 1941 to 1945.

A complicating factor is that a minority of people in every Asian and Pacific country invaded by Japan collaborated with the Japanese military, or even served in it, for a wide variety of reasons, such as economic hardship, coercion, or antipathy to other imperialist powers. Many Koreans served in the Imperial armed forces. The Formosan Army, which was part of the Imperial Japanese Army, was recruited from ethnic Chinese men on Formosa. The Indian National Army, under Subhas Chandra Bose, is perhaps the best-known example of a movement opposed to European imperialism, which was formed during World War II to assist the Japanese military. Prominent individual nationalists in other countries, such as the later Indonesian president, Suharto, also served with Japanese imperial forces. The Burmese nationalist leader Aung San initially sided with the Japanese, forming the Burma National Army, but turned against them in early 1945. In some cases such non-Japanese personnel were also responsible for war crimes committed by the Empire of Japan. B. V. A. Roling, the Dutch justice at the Tokyo trials, noted how "many of the commanders and guards in POW camps were Koreans [as] the Japanese apparently did not trust them as soldiers." Korean guards, he added, were often said to be "far more cruel than the Japanese."[5] One Korean described abject Allied POWs: "now I have seen how depraved and worthless the white man is." For political reasons, many non-Japanese personnel in the Imperial armed forces were never investigated or tried after 1945. In South Korea especially, it is alleged that such people were often able to acquire wealth by participating in exploitative activities with the Japanese military. It is further alleged in South Korea that some former collaborators have covered up "Japanese" war crimes in order to avoid their own prosecution and/or exposure.

It has been argued that acts committed against people subject to Japanese sovereignty cannot be considered "war crimes". The issue of Japan's de facto or de jure sovereignty over places such as Ryukyu (1879–1945)[note 1], Taiwan (1895–1945), and Korea (1910–1945) prior to 1945, is a matter of controversy. Japanese control was accepted and recognized internationally and was justified by instruments such as the Treaty of Shimonoseki (1895, which included China's cession of Taiwan) and the Japan–Korea Annexation Treaty (1910). The legality of the Japan–Korea Annexation Treaty, in particular, is in question because it was not signed by the Korean head of state; it was signed by government ministers. The native populations were not consulted on the changes in sovereignty, nor was there universal acceptance of such annexations. There was ongoing resistance to Japanese invasions and — in any case — war crimes may also be committed during civil wars. (See Korea under Japanese rule and Taiwan under Japanese rule for further details.)

There are also allegations that war crimes were committed even after the Empire of Japan officially surrendered on August 14, 1945. For instance, it is believed that Allied prisoners of war who survived the Sandakan Death Marches, in North Borneo, were killed up to two weeks after the Emperor signed the surrender document.