The Xi'an Incident
On December 12, 1936, Zhang Xueliang (1901-2001) and Yang Hucheng (1893-1949), two patriotic KMT generals, seized Chiang Kai-shek by force in Xi'an, capital city of Shaanxi Province, in an effort to pressurize him into resisting the Japanese aggression. This was known as the Xi'an Incident, or the Double 12th Incident.
In 1935, in the face of expanding Japanese imperialist aggression, the CPC published a An Appeal to All Fellow Countrymen for Resistance Against Japan and for National Salvation (the August 1st Declaration). This advocated a national united front against the Japanese. The call reinvigorated the campaign against the Japanese occupiers, and support for Chiang Kai-shek's slogan of "internal pacification before resistance to foreign invasion" withered.
Zhang Xueliang had more than once tried to persuade Chiang to stop the civil war and join the fight against the Japanese, but every one of his calls had been rejected by Chiang. In early December 1936, Chiang flew to Xi'an and ordered Zhang Xueliang and Yang Hucheng to attack the Red Army in northern Shaanxi. Zhang and Yang decided to resort to force.
Before dawn on December 12, the Northeast Army under Zhang's command and the KMT 17th Route Army under Yang's command detained Chiang, and took into custody dozens of KMT officers and officials from Nanjing such as Chen Cheng (1898-1965) and Wei Lihuang (1897-1960). Zhang and Yang then sent an open telegram to the nation about the mutiny, and made eight proposals including reorganizing the Nanjing government and stopping the civil war. The whole of China and the rest of the world were astounded at this incident.
The CPC had no prior knowledge of the Xi'an Incident. On the very night after the incident, Zhang Xueliang telegraphed the CPC Central Committee calling for consultations. Based on an analysis of the situation at home and abroad, and putting the interests of the Chinese nation above everything else, the CPC leadership agreed to the principle of peaceful settlement of the incident.
On December 17, a CPC delegation headed by Zhou Enlai arrived in Xi'an. They had a sincere discussion with Zhang and Yang, and met with various other interested parties in an effort to achieve peaceful resolution of the incident.
Thanks to the joint efforts of Zhou, Zhang and Yang, and after days of negotiation, Chiang was forced to make six promises. These included commitments to end the suppression of the Communists, and to ally with the Red Army to resist Japan.
The Xi'an Incident occurred just as the objective conditions for renewed KMT-CPC cooperation were ripening, and it helped push those conditions to fruition. The peaceful settlement of the incident saw a dramatic change in the situation in China. The 10-year civil war came to an opaque end, and China turned its gaze from a domestic war to nationwide resistance against the Japanese aggression.
西安事变
1936年12月12日，国民党爱国将领张学良、杨虎城在陕西西安发动“兵谏”，逼迫蒋介石抗日，史称西安事变，亦称“双十二事变”。
面对日本帝国主义的步步紧逼，1935年，中国共产党发布《为抗日救国告全体同胞书》（即《八一宣言》），提出抗日民族统一战线的主张。全国人民的抗日运动进入新的高潮，蒋介石的“攘外必先安内”的政策更加不得人心。张学良曾多次劝谏蒋介石停止内战、一致对外，都被拒绝。
1936年12月初，蒋介石到西安迫令张学良、杨虎城立即率部开赴陕北前线“剿共”。在这种情况下，张学良、杨虎城决定发动“兵谏”。12月12日凌晨，东北军和第十七路军协同行动，扣押了蒋介石，囚禁了陈诚、卫立煌等几十名国民党军政要员，随即通电全国，提出改组南京政府、停止一切内战等八项抗日主张。这便是震惊中外的西安事变。
中国共产党在事变前没有与闻此事。事变爆发后，张学良当夜致电中共中央，希望听取中共意见。中共中央分析了国内外形势，以中华民族利益的大局为重，确定了用和平方式解决事变的方针。12月17日，以周恩来为首的中共代表团到达西安，与张学良、杨虎城恳切会谈，并接见各方人士，力争和平解决西安事变。由于周恩来与张学良、杨虎城的共同努力，经过谈判，迫使蒋介石作出了“停止剿共，联红抗日”等六项承诺。
西安事变在国共两党重新合作的客观形势渐次成熟的时候，起了促成这个合作的作用。西安事变的和平解决，成为时局转换的枢纽。从此，中国十年内战的局面基本结束，中国由此实现了从国内战争到全国抗战的伟大转变。