What was the origin of the rise of the the communist party?

An attempt to reestablish an empirical regime in 1912 failed, leaving a politically fragmented country. In various regions Warlords exercised control over their territories. The nation was unified again in 1920, ruled by one-party -the Kuomintang. The Sino-Japanese War of 1937–1945 (which was part of World War II) forced an alliance between the Nationalists and the Communists. With Japan surrendering, China remained victorious (however financially drained.) Continued distrust between the Nationalists and the Communists led to a civil war. In 1947 a constitutional rule was established, but due to the ongoing Civil War many provisions of it were never implemented in the mainland. The Communist Party of China (CCP) won the civil war and gained control of most of Mainland China.