Northeast Flag Replacement and Nominal Unification

In April 1927 Chiang Kai-shek founded the National Government in Nanjing. While “splitting from and purging the Communists” and suppressing worker and peasant movements, it continued the Northern Expedition. In April 1928 Chiang allied with regional power-holders such as Feng Yuxiang, Yan Xishan and Li Zongren, and attacked the Fengtian warlord Zhang Zuolin with four army groups. In June the expedition reached the Beijing–Tianjin area, and Zhang was forced out of Beijing and back to the Northeast. As Zhang retreated by train beyond the Great Wall, Japan's Kwantung Army blew up his train at Huanggutun near Shenyang; he was gravely wounded and soon died, in the “Huanggutun Incident”. His son Zhang Xueliang succeeded as Commander-in-Chief of Northeast Security. Despite Japanese obstruction and threats, on 29 December 1928 he telegraphed that the Northeast would “abide by the Three Principles of the People, obey the National Government, and change flags”, the “Northeast Flag Replacement”. It marked the end of Beiyang warlord rule and the nominal unification of China under the Nanjing government, and also frustrated Japan's plot to split off the Northeast. But conflicts among the Kuomintang's new warlords remained sharp, and each faction kept its own army. From 1929 to 1930 Chiang fought several wars with regional leaders such as Feng Yuxiang, Yan Xishan and Li Zongren, the largest being the Central Plains War of 1930, which Chiang won. The Nanjing government imposed one-party rule at home, suppressing Communists and revolutionary masses, while also carrying out some economic construction, such as the 1935 currency reform that unified the currency.