In December 1936, Chiang was captured by General Chang Hsüeh-liang in what is now called the [[Xi'an Incident]]. The captors tried to force Chiang to stop fighting the Communists and to unite with them in fighting Japan. After lengthy negotiations, Chiang was released. The [[Second United Front]] between KMT and Communist leaders was formed soon afterward. This tentative truce between to the two parties was always uneasy and actual cooperation on a united military front was rare.