He was sowing the seeds of the Xi'an Incident. On December 12, 1936 Chang and General Yang Hu-cheng detained Chiang Kai-shek in Xi'an hoping to force Chiang to work with the communists to fight against the Japanese.
民國二十五年十二月十二日，張學良與楊虎城在西安扣留蔣介石，逼蔣與中共合作抗日，史稱「西安事變」。