become more acute. The attacks on America's naval base at Pearl Harbor and other American possessions in the Pacific protected the main move southwards.
Japan's smashing victories at sea and on land in the Russo-Japanese War of 1904-1905 signified Japan's rise as a military power in Asia. The Japanese armed forces were seen as the principal guardians of Japan's national essence (kokutai) and the emperorship which was believed to be of divine origin. Ultranationalist secret societies and elements in the Army favored expansion into Manchuria, Inner Mongolia and even Siberia as solutions to Japan's overpopulation and need for natural resources. According to Hane (2001), the Portsmouth Treaty of 1905 which confirmed only southern Manchuria and southern Sakhalin Island as being within Japan's sphere of influence triggered "violent [public] opposition" (p. 190).
During the Russian Civil War, Japan mounted a large (100,000 troops) Siberian Expedition (1918-1922). Bix (2000) said its purpose was "to stop the spread of the Russian Revolution and establish a buffer state in eastern Siberia (p. 45)." In 1925 Japan agreed to withdraw from Northern Sakhalin but retained coal and oil concessions there, which it only relinquished under the 1941 Neutrality Pact.
Until the onset of the Great Depression which severely damaged the Japanese economy, the expansionist tendencies of ultranationalist elements in the Army and elsewhere were largely held in check by senior statesmen, the genro, the bureaucracy and business interests. However, in September 1931 radical right-wing middle-level officers in the Kwantung Army provoked the Mukden Incident (an explosion on the Chinese South Manchurian Railway) which led to Japan's establishment of the puppet state of Manchuko in 1932 and its withdrawal in February 1933 from the League of Nations which condemned Japan's actions. Through intimidation, assassinations of several Japanese Prime Ministers and o...