The Japanese have a long history of barbarism in war.
"In July 1937, the second Sino-Japanese War broke out. A small incident was soon made into a full scale war by the Kwantung army which acted rather independently from a more moderate government. The Japanese forces succeeded in occupying almost the whole coast of China and committed severe war atrocities on the Chinese population, especially during the fall of the capital Nanking. However, the Chinese government never surrendered completely, and the war continued on a lower scale until 1945."