After completing military training with the Japanese Army, he returned to China in 1911 and took part in the revolution against the Manchus (see Ch'ing). Chiang was active (1913-16) in attempts to overthrow the government of Yüan Shih-kai. When Sun Yat-sen established (1917) the Guangzhou government, Chiang served as his military aide. In 1923 he was sent by Sun to the USSR to study military organization and to seek aid for the Guangzhou regime. On his return he was appointed commandant of the newly established (1924) Whampoa Military Academy; he grew more prominent in the Kuomintang after the death (1925) of Sun Yat-sen.

In 1926 Chiang launched the Northern Expedition, leading the victorious Nationalist army into Hankou, Shanghai, and Nanjing. Chiang followed Sun Yat-sen's policy of cooperation with the Chinese Communists and acceptance of Russian aid until 1927, when he dramatically reversed himself and initiated the long civil war between the Kuomintang and the Communists. By the end of 1927, Chiang controlled the Kuomintang, and in 1928 he became head of the Nationalist government at Nanjing and generalissimo of all Chinese Nationalist forces. Thereafter, under various titles and offices, he exercised virtually uninterrupted power as leader of the Nationalist government.

In 1936 Gen. Chang Hsüeh-liang siezed him at Xi'an, to force him to terminate the civil war against the Communists in order to establish a united front against the encroaching Japanese. Despite the resultant truce, Chiang's release, and the 1937 outbreak of the Second Sino-Japanese War, the agreement between Nationalists and Communists soon broke down. By 1940 Chiang's best troops were being used against the Communists in the northwest. After the Japanese took Nanjing and Hankou, Chiang moved his capital to Chongqing.

As the Sino-Japanese War merged with World War II, Chiang's international prestige increased. He attended the Cairo Conference (1943) with Franklin Delano Roosevelt and Winston Churchill. He and his wife, Soong Mei-ling (see Soong, family), were the international symbols of China at war, but Chiang was bitterly criticized by Allied officers, notably Joseph W. Stilwell, and argument raged over his internal policies and his conduct of the war.

After the war ended Chiang failed to achieve a settlement with the Communists, and civil war continued. In 1948 Chiang became the first president elected under a new, liberalized constitution. He soon resigned, however, and his moderate vice president, Gen. Li Tsung-jên, attempted to negotiate a truce with the Communists. The talks failed, and in 1949 Chiang resumed leadership of the Kuomintang to oppose the Communists, who were sweeping into S China in strong military force and reducing the territories held by the Nationalists.