Lying at the juncture of the Chinese, Japanese and Russian spheres of influence, Manchuria has been a hotbed of conflict since the late-19th century. The Russian Empire established control over the northern part of Manchuria in 1860 (Beijing Treaty); it built (1897-1902) the Chinese Eastern Railway to consolidate its control. Disputes over Manchuria and Korea led to the Russo-Japanese War of 1904–1905. The Japanese invaded Manchuria in 1931, setting up the puppet state of Manchukuo which became a centerpiece of the fast-growing Empire of Japan. The Soviet invasion of Manchuria in August 1945 led to the rapid collapse of Japanese rule, and the Soviets restored the region of Inner Manchuria to Chinese rule: Manchuria served as a base of operations for the Mao Zedong's People's Liberation Army in the Chinese Civil War, which led to the formation of the People's Republic of China in 1949. In the Korean War of 1950-1953, Chinese forces used Manchuria as a base to assist North Korea against the United Nations Command forces. During the Sino–Soviet split Manchuria became a matter of contention, escalating to the Sino–Soviet border conflict in 1969. The Sino-Russian border dispute was resolved diplomatically only in 2004.