the CCP army mostly fought against the Japanese puppet army for the entire duration of the war. the Japanese army defended the cities, strategic locations, lines of communications, and the frontlines against the KMT govt army. they rarely entered the vast countrysides, and deployed the puppet army there where there was the CCP army. the poorly trained and unmotivated puppet army was quite ineffective against the CCP army. that’s how the CCP took huge amount of territory during the war.