When the Japanese Empire went to war with the Allies in December 1941, it had already been fighting in China for 10 years and set up 'puppet' governments designed to rule on behalf of the Japanese while firmly under their overall control. Chinese puppet soldiers ranged from the well-drilled and trained regular Army of the Last Emperor of China, Pu Yi, to the irregular Mongol cavalry who served alongside Japanese troops in the 'secret war' waged in the Mongolian hinterlands. The troops were dismissed as traitors by the Chinese fighting the Japanese. The fact that so many Chinese were willing to fight for the Japanese was embarrasing to all sides, and for this reason has been largely ignored in previous histories of the war in the East.