File photo taken on July 9, 2015 shows a coal mine pit cramed with skulls and bones of Chinese forced miners working for Japan during the World War II, at a memorial in Datong, north China's Shanxi Province. Japan invaded northeast China in 1931 and conducted a full-scale invasion in 1937. By the end of World War II, millions of Chinese forced laborers had been enslaved by Japanese invaders to toil under harsh conditions at mines and factories in northeast China and Japan. Those laborers were under close watch and suffered inhumane treatment. Many of them died from malnutrition, illness, physical abuse and plain murder. (Xinhua/Zhan Yan)