By the end of 1935, Jiang's lack of resistance enabled the Japanese to occupy Manchuria and Rehe (Jehol) (an old province made up of parts of today's northeast Hebei [Hopeh], southwest Liaoning, and southeast Inner Mongolia). The Japanese were about to advance into Chaha'er (Chahar, an old province west of Rehe comprising the northern part of today's Hebei) and Suiyuan (a defunct province west of Chaha'er comprising the central part of current Inner Mongolia). Under steadily mounting pressure, Jiang stubbornly refused to declare war on Japan. This stance led some leaders to conclude that coercion was the only way to force him to reverse his stance, precipitating the Xi'an (Sian) Incident of December 1936 in Shaanxi (Shensi) Province.
On 4 December 1936, Jiang flew to Xi'an to discuss with Zhang Xueliang (Chang Hsüeh-liang) and Yang Hucheng (Yang Hu-ch'eng), commanders of the Northeastern and Northwestern Armies, respectively, the last "extermination campaign" against the Chinese Communists, who had settled in Yan'an (Yenan), north of Xi'an, a year earlier after the 1934–1935 Long March. Zhang seized this opportunity to try to persuade Jiang to cooperate with the Chinese Communists in establishing a united front against the Japanese. Unable to convince Jiang, Zhang and Yang decided to stage a coup. In the early morning of 12 December, Zhang marched his army to Lintong (Lin-t'ung), west of Xi'an, where Jiang's villa was located, and kidnapped Jiang, while Yang seized all Jiang's establishments and personnel in Xi'an.
Zhang took Jiang back to Xi'an, where he was held in detention, then invited the Chinese Communists to visit to negotiate for a united front against the Japanese. The Chinese Communist delegation included Zhou Enlai (Chou En-lai), Li Kenong (Li K'o-nung), and Ye Jianying (Yeh Chien-ying). Madam Jiang Soong Meiling traveled from Nanjing (Nanking), Jiangsu (Kiangsu) Province, to represent her husband in negotiations with Zhou. Their discussion was based on Zhang's proposal for ending the civil war and forming a united front to resist the Japanese invasion, to which Jiang finally gave his verbal agreement on Christmas Eve. On 25 December, Jiang was released, and he flew back to Nanjing, immediately beginning work on a united front for the forthcoming Sino-Japanese War.
Zhang, who accompanied Jiang back to Nanjing, was arrested by Jiang's agents, tried on charges of insubordination, and sentenced by a military court to a 10-year prison term. On 4 January 1937, Jiang granted him amnesty and placed him under the National Military Council's close surveillance, a face-saving measure. The next day, Jiang relieved Yang all of his military posts, and he still held him in detention at year's end. Despite the sacrifice by the individuals involved in the coup, their action was widely appreciated as a pivotal point in the bitter anti-Japanese resistance effort of the Chinese.
Coble, Parks M. Facing Japan: Chinese Politics and Japanese Imperialism, 1937–1941. Cambridge, MA: Harvard University Press, 1991.; Dryburgh, Marjorie. North China and Japanese Expansion, 1933–1937. Richmond, UK: Curzon Press, 2000.; Wang, Ernestine H. "Chang Hsueh-liang and the Chinese Communists, 1934–1936." Master's thesis, Georgetown University, 1982.; Wu, Tien-wei. The Sian Incident: A Pivotal Point in Modern Chinese History. Ann Arbor: University of Michigan Press, 1978.