Why did Li Zongren, who was born in Guangxi warlord, force Chiang to step down and even ascend to the presidency?

In fact, as a veteran figure in the Kuomintang, Li Zongren participated in the League very early. He took part in the war to defend his country, the war to defend his country and the war between Guangdong and Guangxi, and gradually pushed himself to the high position of warlords in Guangxi. With political and tactical talent, Li Zongren quickly became a duck to water in the army, and his influence developed step by step.