In 1917, as China's southern provinces rebelled, Sun Yat-sen began to reassemble remnants of the KMT. Sun, determined to defeat the warlords, began to train an army with the help of Canton warlord Chen Qiu-ming. 

In 1923, with prompting from the Soviet Union, the First United Front was formed. It was an alliance between the KMT and the CCP, with the aim of eradicating warlords, imperialists, and the feudal autocracy in China. Under the First United front, the CCP renounced its autonomy and joined the KMT, which was headquarted in Canton. 

In 1923 the Sun-Joffe Manifesto was signed between the KMT and the USSR. In this agreement between Sun and Comintern agent Adolf Joffe, in return for weapons and training, Sun would accept Communist members into the KMT. 

In 1924 the Whampoa Military Academy in Guangzhou was founded by the KMT with Soviet aid. Chiang Kai-shek, who had trained in the Soviet Union in 1924 and studied Russian military methods, became Whampoa’s first commandant, while a young Communist and future Premier of the People's Republic of China, Zhou Enlai, was appointed director of the political department of the Academy.

On March 12, 1925, Sun died of liver cancer, setting off a power struggle between Chiang Kai-shek and Wang Jingwei, a left-wing KMT member, for control over the KMT. Chiang emerged as the leader of the KMT, but the United Front had already begun to deteriorate. The union was only held together by the two parties' mutual resentment of the warlords and of imperialism. Although Chiang doubted Sun's policy of alliance with the Soviet Union and CCP, he still needed aid from the Soviet Union, so he could not break up the alliance yet.