China's 'Communist Revolution' was the Chinese Civil War. The leader of the Communist group was Mao Zedong. The leader of the standing, nationalist government was Chiang Kai-Shek.
The Collapse of the Qing Dynasty in 1911.
The enormity of China and the inabilty of the Kuomintang to control it.
The Japanese invasion and the opportunity it gave Mao to use his army.