A conflict on the Chinese mainland between combined nationalist and communist Chinese forces and Japan. China had been the target of Japanese expansionism since the late 19th century, and after the Mukden Incident of 1931 full-scale war was only a matter of time. Hostilities broke out, without any formal declaration of war by either side, after a clash near the Marco Polo bridge just west of Beijing in 1937. The Japanese overran northern China, penetrating up the Yangtze and along the railway lines, capturing Shanghai, Nanjing, Guangzhou, and Hankou by the end of 1938. In the ‘Rape of Nanjing’, over 100,000 civilians were massacred by Japanese troops. The invaders were resisted by both the Kuomintang army of the nationalist leader Chiang Kai-shek and the communist 8th Route Army, the former being supplied after 1941 by Britain and the USA. By the time the conflict had been absorbed into World War II, the Sino–Japanese War had reached a state of near stalemate, Japanese military and aerial superiority being insufficient to overcome tenacious Chinese resistance and the problems posed by massive distances and poor communications. The Chinese kept over a million Japanese troops tied down for the entire war, inflicting a heavy defeat upon them at Jiangxi in 1942 and successfully repelling a final series of offensives in 1944 and 1945. The Japanese finally surrendered to Chiang Kai-shek on 9 September 1945, leaving him to contest the control of China with Mao Zedong’s communist forces.