On July 7, 1937, forces of the Republic of China's National Revolutionary Army and Japan's Imperial Japanese Army engaged in combat with each other at Wanping and the Marco Polo Bridge (also known as the Lugou Bridge). While Japanese troops were allowed to be stationed at certain points in China as well as conduct military exercises freely with the country as part of Boxer Protocol, Imperial Japan had deployed between 7000-15000 men within China's borders by July 1937, far more than the European powers which were also part of the Boxer Protocol. This combined with the Japanese invasion of Manchuria in 1931 and subsequent establishment of the puppet state of Manchukuo served to drastically elevate tensions between China and Japan. Tensions evolved into open hostilities on the night of July 7, 1937, when Chinese and Japanese troops exchanged fire at Wanping (near Beijing). By early morning of July 8, reinforcements to both sides had arrived and full-scale hostilities began shortly after the return of the mayor of Wanping, Wang Lengzhai, from a failed attempt to resolve the situation diplomatically. The Chinese defenders successfully held their ground, including the bridge, and a ceasefire arrangement was reached on July 9. However, Japanese forces continued to violate the ceasefire and continued to attack not only Wanping but also Beijing, resulting in the battle of Beiping-Tianjin and the opening salvo of the Second Sino-Japanese War which would in turn become a significant part of the Second World War.