中原大戰
In 1930, he fought with warlords Feng Yuxiang and Yan Xishan in the Central Plains War against Chiang Kai-shek's government. Sun's forces were involved in a major friendly fire incident during this war, as they mistakenly fired on Feng's troops at Shangqiu. The two warlords almost went to war over this issue. As the conflict turned against the warlord alliance, Sun's army increasingly suffered from mass desertion, so that he "desperately" launched recruitment campaigns in northern Henan and southern Hubei while the fighting was still ongoing. Realising that the Central Plains War was lost, Sun eventually retreated with his remaining army from the front at Bozhou, and joined the Nationalist-allied forces of Zhang Xueliang. He moved to Shanxi, where his men were reorganized as 40th Division and garrisoned at Jincheng.