In 1937, Japan was trying to apply controls over China. It
was especially hostile to China's communists, without realizing that it
was giving them new opportunity. China's ruler, Chiang Kai-shek,
diverted his attention from fighting communists to fighting Japan.
The communists reorganized their army, advanced eastward against the
Japanese and began guerrilla warfare. And fighting against Japan's
occupation helped advance the communists in the eyes of the public.