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 Beiping and was of considerable strategic importance. Prior to July 1937, Japanese forces had repeatedly demanded the withdrawal of the Chinese forces stationed at this place.