The Chinese Civil War was a civil war fought between Mao Zedong's communist forces and Jiang Jieshi’s nationalists. This war was fought from 1927 to 1950. Mao's Communist forces triumphed, giving birth to the People's Republic of China, or PRC, in 1949. Jiang Jieshi and his nationalist supporters fled to the island of Taiwan. With no opposition left, the communists were in control, causing China to finally be united.
For a quick overview of Jiang Jieshi, including facts on who he was, his role in the Chinese Civil War, and the Chinese people's views on him, click the link below. Cultural China, Historical Figures: Chiang Kai-shek (Jiang Jieshi is another name that he is known by)
This website provides some background knowledge about the events leading up to the civil war. Fact Monster: Chinese Civil War