During the Marco Polo Bridge Incident on 8 July 1937, the Japanese China Garrison Army attacked the walled city of Wanping (宛平鎮) after an ultimatum to allow its forces to search for an allegedly missing soldier had elapsed.

Wanping, in the neighborhood of Lugou Bridge, was on the main railway line west of Beijing and was of considerable strategic importance.

[6] Meanwhile, the Japanese civilian government of Prime Minister Konoe in Tokyo held an extraordinary cabinet meeting on 8 July, and resolved to attempt to defuse hostilities and settle the issue diplomatically.

This mobilization was strongly opposed by General Kanji Ishihara on the grounds that an unnecessary escalation in the conflict with China was endangering Japan's position in Manchukuo vis-à-vis the Soviet Union.

At Ishihara's urging, the deployment was delayed while Konoe used his personal contacts with Japanese acquaintances of Sun Yat-sen in an effort to establish a direct diplomatic settlement with the Kuomintang central government in Nanjing.

The Japanese then issued an ultimatum to General Song demanding the withdrawal of all Chinese forces from the outskirts of Beijing to the west of the Yongding River within 24 hours.

[7] On 28 July, the IJA 20th Division and three independent combined brigades launched an offensive against Beijing, backed by close air support.

[8] However, this was only a temporary respite, and by nightfall General Song admitted that further combat was futile and withdrew the main force of Chinese 29th Army south of the Yungging River.

Tianjin Major General Zhang Zizhong was left in Beiping to take charge of political affairs in Hebei and Chahar provinces with virtually no troops.

General Huang Wei-kang's brigade defended the Taku Forts gallantly and also attacked a nearby Japanese airfield, destroying many aircraft.