Tensions between Japan and China reached its breaking point on 7 July 1937. Under the terms of the Boxer Protocol, Japan was authorized to station troops near Beijing to maintain security and open communications between the capital city and the port of Tianjin. A supplemental agreement authorized Japan to conduct military maneuvers in the region by informing the Chinese government. By 1937, Japan had nearly 15,000 soldiers stationed in China, far more than the small detachments of European soldiers serving in China per the Boxer Protocol. On the night of 7 July, Japan launched a military exercise outside of their base in Fengtai. At 11:00 p.m. Japanese and Chinese troops exchanged fire near the town of Wanping.
The mayor of Wanping, Wang Lengzhai, arrived at the Japanese headquarters around 2:00 a.m. to conduct negotiations. This effort proved fruitless, and the Japanese demanded to enter the town to investigate the incident. By 4:00 a.m. both sides were bolstering their forces near the town. Japanese forces attacked the Marco Polo Bridge an hour later. The Chinese had moved 100 troops to hold the bridge, after a heavy firefight and with the aid of reinforcements repulsed the Japanese advance. Continued efforts were made to de-escalate the conflict. Despite the continued calls for a ceasefire, the Japanese garrison commander, Gen. Masakazu Kawabe ordered his artillery to shell Wanping for the next three hours.
The Japanese would again shell the city on 9 July, followed with an armored assault on the city. On 11 July, the Imperial Japanese Army General Staff authorized the deployment of an infantry division, two brigades, and 18 air squadrons to the Beijing-Tianjin area. The Japanese command gave their troops free passage to pacify Chinese resistance in the area. After three weeks of fighting the Chinese forces in the region were forced to withdraw. After capturing Beijing and the Taku Forts in Tianjin, the Japanese government opened up negotiations with the Chinese government, citing “Japan wants Chinese cooperation, not Chinese land.” This lull in the conflict would not last long. Following the shooting of a Japanese naval officer in Shanghai, full scale warfare once again erupted.