Yang Hucheng in the context of "Song Qiyun"

The Xi'an Incident was a Chinese political crisis that lasted from 12 to 26 December 1936. Soldiers of the Northeastern Army under the command of General Zhang Xueliang arrested Chiang Kai-shek, the leader of the Nationalist government of China, while the latter was in Xi'an to review the troops. Zhang demanded that Chiang agree to a ceasefire in the Chinese Civil War so that the Nationalist government could ally with the Chinese Communist Party (CCP) against Japanese expansionism. Negotiations were held between Chiang and the CCP, resulting in verbal agreement on the broad outlines of an alliance. After Chiang was released, he publicly renounced the terms he had agreed to in captivity, but secretly continued the negotiations that would result in the Second United Front.

The Xi'an Incident followed months of secret negotiations between the CCP and the Nationalists. Only minor progress had been made by December 1936. However, the CCP had also been negotiating directly with the Nationalist armies that surrounded it, including the Northeastern Army. These negotiations had been much more successful. The CCP formed a secret alliance with Zhang's Northeastern Army and Yang Hucheng's Northwestern Army that aimed to see the civil war ended and a war of national liberation begun against Japan. With encouragement from the CCP, Zhang repeatedly but unsuccessfully pressured Chiang to agree to a ceasefire with the CCP. After Chiang gave Zhang an ultimatum to either attack the Communists or be reassigned, Zhang decided to take Chiang hostage and force a settlement.

The Guominjun (traditional Chinese: 國民軍; simplified Chinese: 国民军; pinyin: Guómínjūn; Wade–Giles: Kuo-min-chün), also known as the Kuominchun, abbreviated as GMJ and KMC, was a military faction founded by Feng Yuxiang, Hu Jingyi and Sun Yue during China's Warlord Era. The KMC had control of much of Northwest China, including Shaanxi, Chahar and Suiyuan, hence its other name, the Northwest Army (西北軍; not to be confused with the later army of the same name under Yang Hucheng).