Angered by Chiang Kai-shek's policy of attaching priority to fighting the Communists over the Japanese, KMT forces mutiny against Chiang in December 1936. In what is later named the "Xi'an Incident," KMT generals Zhang Xueliang and Yang Hucheng kidnap Chiang and hold him hostage until he agrees to cooperate with the CCP to form a "united front" against the Japanese. Chiang is released after a ceasefire is called. Cooperation between the CCP and KMT remains difficult.