The Chinese Civil War was a civil war in China fought between forces loyal to the Kuomintang (KMT)-led government of the Republic of China, and forces loyal to the Communist Party of China (CPC). The war began in August 1927, with Chiang Kai-Shek's Northern Expedition, and essentially ended when major active battles ceased in 1950. The conflict eventually resulted in two de facto states, the Republic of China (ROC) in Taiwan and the People's Republic of China (PRC) in mainland China, both officially claiming to be the legitimate government of China.
The Chinese Civil War began again shortly after the Japanese were pushed out off China in the final years of Word War II. Throughout the remainder of the 1940s, Mao Tse-Tung gained on Chiang Kai-Shek's forces, until, in October 1949, just two months after the end of the Japanese War, Mao and his Reds pushed Chiang's forces off of the Chinese mainland.
The U.S. had backed Chiang, and refused to recognize Mao. For a time, U.S. PresidentJoe Steele had considered using atomic bombs to support Chiang, as they'd effectively ended the Japanese War. However, the Soviet ambassador to the U.S., Andrei Gromyko, suggested that any U.S. atomic attack in China might be met with a Soviet atomic attack in Europe.
The Chinese Civil War was interrupted by the invasion of Japan.
As the leader of China, Chiang Kai-Shek was supposed to be fighting the Japanese. However, many people (Communists especially) believed China's only real hope lay with Mao Tse-Tung. Even the Japanese, while worried about Chiang's troopers, were more worried about the guerrilla tactics of the Communists throughout the war. Thus, the Civil War continued on indirectly.