"The winds began to change his way after Stalin gave his guidance on this incident. Stalin believed that Chiang's execution would not be beneficial to either Chinese resistance to Japan or Soviet interests in the Far East. Desperately in need of Soviet aid, Mao relented to Stalin’s opinion and showed his enthusiasm for peace talks. On 17 December 1936, the CPC delegation was sent to Xian and met with Zhang and Yang to find a peaceful resolution. On 22 December 1936, Madam Chiang and her elder brother T.V. Soong flew to Xian to meet the CPC delegation, Zhang, and Yang. On 24 December 1936, the parties reached an agreement to establish a united front against Japan and to release prisoners accused of inciting anti-Japanese riots. The next day Chiang and his entourage were released. Zhang escorted him back to Nanjing, although Zhou expressed his concern."
（http://en.wikipedia.org/wiki/Xi%27an_Incident）
（http://en.wikipedia.org/wiki/Xi%27an_Incident）