n 1937.
Yan was aware of the threat posed by the Japanese; and, in order to defend against the impending Japanese invasion of Shanxi, Yan entered into a secret "united front" agreement with the Communists in November 1936. After concluding his alliance with the Communists he allowed agents under Zhou Enlai to establish a secret headquarters in Taiyuan. Yan, under the slogan "resistance against the enemy and defense of the soil" attempted to recruit young, patriotic intellectuals to his government from across China, so that by 1936 Taiyuan became a gathering point for anti-Japanese intellectuals who had fled from Beijing, Tianjin, and Northeast China. A representative of the Japanese army, speaking of the final defense of Taiyuan, said that "nowhere in China have the Chinese fought so obstinately".
From the Japanese occupation of Taiyuan to the Japanese surrender in 1945, the Japanese continued to develop Taiyuan's industries and resources. After the Japanese army in Shanxi surrendered to Yan Xishan, 10,000-15,000 Japanese troops, including both enlisted men and officers, decided to fight for Yan rather than return to Japan. Yan also retained the services of experienced and foreign-educated Japanese technicians and professional staff brought into Taiyuan by the Japanese to run the complex of industries that they had developed around Taiyuan.
Taiyuan was the last area in Shanxi to resist Communist control during the final stages of the Chinese Civil War. The city fell on April 22, 1949, after the Communists surrounded Taiyuan and cut it off from all means of land and air supply, and taking the city required the support of 1,300 pieces of artillery. The fall of Taiyuan was one of the few examples in the Chinese Civil War in which Nationalist forces echoed the defeated Ming loyalists who had, in the 17th century, brought entire cities to ruins resisting the invading Manchus. Many Nationalist officers committed suicide when the city fell. The dead
