the Japanese army didn't have adequate troops for the large conquered lands of China. therefore they strategically used their troops in the cities, transport lines, and important points, and used puppet troops in the unimportant vast rural countrysides which were the bases of the CCP. the puppet army was ineffective and useless. the CCP was given a free rein to build up their army and expand their political influence there. the Japanese army almost only fought the conventional battles against the KMT government army, the puppet army almost only fought small battles and skirmishes against the CCP army, throughout the war. to put it simply, few Japanese troops entered the CCP controlled areas, where the hell the CCP killed so many Japanese troops which they kept boasting about until now ?