After World War I, the Western Powers, influenced by Wilsonian ideology, attempted an effort at general disarmament. At the Washington Naval Conference of 1921–1922, the Great Powers met to set limits on naval armament. The Five Power Naval Limitation Agreement worked out in Washington limited competition in battleships and aircraft carriers to a ratio of 5:5:3 for the United Kingdom, the United States, and Japan respectively. Japanese ultra-nationalists viewed this as an attempt by Western powers to curb Japanese expansionism in an area of the globe over which they had no interest. But, those in power in Japan readily agreed to the disarmament, realizing that the global taste for war had been soured after the First World War and knowing that, the ratio was sufficient to maintain hegemony in the Pacific.
In 1924, however, friendly U.S.-Japanese relations were torpedoed by the Japanese Exclusion Act. The act closed off Japanese immigration to the United States and dropped Japanese immigrants to the level of other Asians (who were already excluded). The overwhelming reaction in Japan, both at the highest levels and in mass rallies that reflected angry public opinion, was hostile and sustained. Commentators suggested the opening guns of a race war and called for a new buildup of the Japanese armed forces.[4]
From 1928 to 1932, domestic crisis could no longer be avoided. As the left was vigorously put down by the state, the economic collapse brought a new hardship to the people of Japan. Silk and rice prices plummeted and exports decreased 50%. Unemployment in both the cities and the countryside skyrocketed and social agitation came to a head.[citation needed]
Meanwhile, the London Naval Treaty was ratified in 1930. Its purpose was to extend the Washington Treaty System. The Japanese government had desired to raise their ratio to 10:10:7, but this proposal was swiftly countered by the United States. Thanks to back-room dealing and other intrigues, though, Japan walked away with a 5:4 advantage in heavy cruisers,[5] but this small gesture would not satisfy the populace of Japan which was gradually falling under the spell of the various ultra-nationalist groups spawning throughout the country. As a result of his failings regarding the London Naval Treaty, Prime Minister Hamaguchi Osachi was shot on November 14, 1930 by an ultranationalist and died in 1931.
By this time, the civilian government had lost control of the populace. A New York Times correspondent called Japan a country ruled by "government by assassination."[6] The army, moving independently of the proper government of Japan, took the opportunity to invade Manchuria in the Summer of 1931.
Since the Russo-Japanese War of 1905, Japan had maintained a military presence in Manchuria. After a small explosion on the tracks of a Japanese railway, north of Mukden, the Japanese army mobilized the Kwantung Army and attacked Chinese troops. The Minseito government, headed by Hamaguchi's successor, Wakatsuki Reijirō was unable to curb the army's offensive. The Kwantung Army conquered all of Manchuria and set up the puppet state of Manchukuo. The Diet, now dominated by army officials, voted to withdraw from the League of Nations. The first seeds of the coming conflict had been sown.