What Was the Marco Polo Bridge Incident?

On July 7, 1937, Japanese and Chinese troops clashed at the Marco Polo Bridge beginning the Second Sino-Japanese War. This in effect was the beginning of WWII in Asia. An excerpt from the article:

"The Incident
In the early summer of 1937, Japan began to carry out military training exercises near the bridge. They always warned the local inhabitants, to prevent panic, but on July 7, 1937, the Japanese commenced training without prior notice to the Chinese. The local Chinese garrison at Wanping, believing that they were under attack, fired a few scattered shots, and the Japanese returned fire. In the confusion, a Japanese private went missing, and his commanding officer demanded that the Chinese allow the Japanese troops to enter and search the town for him. The Chinese refused. The Chinese army offered to conduct the search, which the Japanese commander agreed to, but some Japanese infantry troops tried to push their way into the town regardless. Chinese troops garrisoned in town fired on the Japanese and drove them away.

With events spiraling out of control, both sides called for reinforcements. Shortly before 5 am on July 8, the Chinese allowed two Japanese investigators into Wanping to search for the missing soldier. Nonetheless, the Imperial Army opened fire with four mountain guns at 5:00, and Japanese tanks rolled down the Marco Polo Bridge shortly thereafter. One hundred Chinese defenders fought to hold the bridge; only four of them survived. The Japanese overran the bridge, but Chinese reinforcements retook it the following morning, July 9.

Meanwhile, in Beijing, the two sides negotiated a settlement of the incident. The terms were that China would apologize for the incident, responsible officers on both sides would be punished, Chinese troops in the area would be replaced by the civilian Peace Preservation Corps, and the Chinese Nationalist government would better control communist elements in the area. In return, Japan would withdraw from the immediate area of Wanping and the Marco Polo Bridge. Representatives of China and Japan signed this accord on July 11 at 11:00 am.

The national governments of both countries saw the skirmish as an insignificant local incident, and it should have ended with the settlement agreement. However, the Japanese Cabinet held a press conference to announce the settlement, in which it also announced the mobilization of three new army divisions, and harshly warned the Chinese government in Nanjing not to interfere with the local solution to the Marco Polo Bridge Incident. This incendiary cabinet statement caused Chiang Kaishek's government to react by sending four divisions of additional troops to the area.

Soon, both sides were violating the truce agreement. The Japanese shelled Wanping on July 20, and by the end of July, the Imperial Army had surrounded Tianjin and Beijing. Even though neither side likely had planned to go into an all-out war, tensions were incredibly high. When a Japanese naval officer was assassinated in Shanghai on August 9, 1937, the Second Sino-Japanese War broke out in earnest. It would transition into the Second World War, ending only with Japan's surrender on September 2, 1945."