Xi'an Incident in the context of "Yang Hucheng"

The Second Sino-Japanese War was fought between the Republic of China and the Empire of Japan between 1937 and 1945, following a period of war localized to Manchuria that started in 1931. It is considered part of World War II, and often regarded as the beginning of World War II in Asia. It was the largest Asian war in the 20th century. It is known in China as the War of Resistance Against Japanese Aggression.

On 18 September 1931, the Japanese staged the Mukden incident, a false flag event fabricated to justify their invasion of Manchuria and establishment of the puppet state of Manchukuo. This is sometimes marked as the beginning of the war. From 1931 to 1937, China and Japan engaged in skirmishes, including in Shanghai and in Northern China. Nationalist and Chinese Communist Party (CCP) forces, respectively led by Chiang Kai-shek and Mao Zedong, had fought each other in the Chinese Civil War since 1927. In late 1933, Chiang Kai-shek encircled the Chinese Communists in an attempt to finally destroy them, forcing the Communists into the Long March, resulting in the Communists losing around 90% of their men. As a Japanese invasion became imminent, Chiang still refused to form a united front before he was placed under house arrest by his subordinates who forced him to form the Second United Front in late 1936 in order to resist the Japanese invasion together.

Chiang Kai-shek (31 October 1887 – 5 April 1975) was a Chinese politician, revolutionary, and military commander who led the Republic of China (ROC) from 1928 until his death in 1975. His government was based in mainland China until it was defeated in the Chinese Civil War by Mao Zedong's Chinese Communist Party (CCP) in 1949, after which he continued to lead the ROC government on the island of Taiwan. Chiang served as leader of the Nationalist Kuomintang (KMT) party and the commander-in-chief of the National Revolutionary Army (NRA), which was reorganized into the Republic of China Armed Forces in 1947, from 1926 until his death.

Born in Zhejiang, Chiang received a military education in China and Japan and joined Sun Yat-sen's Tongmenghui organization in 1908. After the 1911 Revolution, he was a founding member of the KMT and head of the Whampoa Military Academy from 1924. After Sun's death in 1925, Chiang became leader of the party and commander-in-chief of the NRA, and from 1926 to 1928 led the Northern Expedition, which nominally reunified China under a Nationalist government based in Nanjing. The KMT–CCP alliance broke down in 1927 following the KMT's Shanghai Massacre, starting the Chinese Civil War. Chiang sought to modernise and unify the ROC during the Nanjing decade, although hostilities with the CCP continued. After Japan's invasion of Manchuria in 1931, his government tried to avoid a war while pursuing economic and social reconstruction. In 1936, Chiang was kidnapped by his generals in the Xi'an Incident and forced to form an anti-Japanese Second United Front with the CCP, and between 1937 and 1945 led China in the Second Sino-Japanese War, mostly from the wartime capital of Chongqing. As the leader of a major Allied power, he attended the 1943 Cairo Conference to discuss the terms for Japan's surrender in 1945, including the return of Taiwan, where he suppressed the February 28 uprising in 1947.

Zhang Xueliang (Chinese: 張學良; June 3, 1901 – October 15, 2001), also commonly known by his nickname "the Young Marshal", was a Chinese general who in 1928 succeeded his father Zhang Zuolin as the commander of the Northeastern Army. He is best known for his role in the Xi'an Incident in 1936, in which he arrested Chiang Kai-shek and forced him to form a Second United Front with the Chinese Communist Party against the Japanese.

In 1928, Zhang, at the time a general in the Northeastern Army, became the commander of the army and leader of the Fengtian clique upon his father's assassination. A reformer sympathetic to nationalist ideas, he completed the official reunification of China by pledging loyalty to the Nationalist government, and used his powerful base to wield significant influence in the politics of the Nanjing decade. Zhang followed Chiang's policy of nonresistance to the Japanese invasions of Manchuria in 1931 and Rehe in 1933, after which he was forced to resign as head of the Northeastern Army.

The Northeastern Army, also known as the Fengtian Army (see terminology), was a Chinese army that existed from 1911 to 1937. General Zhang Zuolin developed it as an independent fighting force during the Warlord Era. He used the army to control Northeastern China (Manchuria) and intervene in national politics. During the mid-1920s the Northeastern Army was the dominant military force in China, but in 1928 it was defeated by the Kuomintang's National Revolutionary Army (NRA) during the Northern Expedition. At the end of that campaign, Zhang Zuolin was assassinated and succeeded by his son Zhang Xueliang. When Xueliang subsequently pledged loyalty to the Kuomintang, the Northeastern Army became part of the NRA and was officially rechristened the "Northeastern Border Defense Force".

Despite being formally part of the NRA, the Northeastern Army remained de facto Zhang Xueliang's personal army. Zhang used the army to exercise considerable political influence during the tumultuous early years of the Nanjing Decade. The Japanese invaded Manchuria in 1931 and forced the Northeastern Army to retreat into northern China. After the army was unable to prevent further Japanese annexations of Chinese territory, Zhang was temporarily removed from command. In 1935, the army was reassigned to the Gansu-Ningxia border area in an attempt to encircle the Chinese Communist Party (CCP)'s base there. Both Zhang and his soldiers resented fighting fellow Chinese while Manchuria was under occupation. They negotiated a covert ceasefire with the CCP and hoped to convince Chiang Kai-shek to endorse a united front against Japan. After Chiang refused, the Northeastern Army kidnapped him and forced him to negotiate with the Communists. Although Chiang eventually agreed to end the civil war and work with the Communists against Japan, Zhang was placed under house arrest and the Northeastern Army was divided and reassigned to other commands.