September 18, 1931
In the Mukden Incident, also known as the Manchurian Incident, renegade members of the Japanese Kwantung Army blew up a section of a Japanese railroad in southern Manchuria as a pretext for overthrowing the local Chinese government affiliated with Chiang Kai-shek. The incident was directly responsible for launching Japan on 14 years of constant warfare which would only finally be brought to an end by nuclear holocaust over Hiroshima and Nagasaki in 1945.
Japan had long sought special rights in Manchuria, dating back to the unsatisfactory settlement of the first Sino-Japanese War in 1895, because it saw Manchuria as vital to the defense of Korea, which in turn was seen as vital to the defense of Japan. But by 1931, many in the Japanese military had begun to feel that the neutrality of Manchuria was increasingly threatened by aggressive Russian posturing in the north and the growing success of Chiang's Nationalist Chinese unification in the south, not to mention the 200,000 troops under Manchurian warlord Chang Hsüeh-liang, who had recently declared his support for Chiang.
Moreover, in response to perceived setbacks such as the withdrawal of Japanese troops from China by the pacifist Hamaguchi government and the perceived humiliation of the 1930 London Naval agreements, many Japanese militarists had already developed a persecution complex in which they saw a vast conspiracy of Japanese pacifists and foreign powers to deprive Japan of a leading role on the world stage, a conspiracy which could only be thwarted by direct and decisive action.
With Hamaguchi out of the way thanks to an assassin's bullet, and the weak Wakatsuki cabinet in "control" of the government in late 1931, the stage was set for just such a decisive blow. On the night of September 18, 1931, members of the Japanese Kwantung Army, stationed in southern Manchuria to guard the Japanese-controlled South Manchurian Railway, acted on the orders of Colonel Itagaki Seishiro and Lieutenant Colonel Ishiwara Kanji by blowing up a section of the railway near the town of Mukden (now known as Shenyang) and then promptly attacking the Mukden garrison as if the Chinese had been responsible.
The Japanese Army's general staff ordered reinforcements into Manchuria from Korea, and by the end of September the Japanese had occupied all of southern Manchuria. The Army then ignored calls by the Wakatsuki government to cease its advance and refer the incident to arbitration by the League of Nations, instead continuing on into northern Manchuria, and meanwhile securing the deposal of Wakatsuki in December. By early 1932, Japanese forces had overrun all of Manchuria, and the puppet-state of Manchukuo was declared on February 18, 1932.
The Japanese army had a relatively easy time taking over Manchuria because Chiang Kai-shek was more concerned with chasing the communists and actually ordered to give way to the Japanese and await the results of an investigation of the Mukden incident by the League of Nations. The League's Lytton Commission ultimately determined that the Japanese were the aggressors and should withdraw back to their original positions, whereupon the new, more military-friendly Japanese government promptly took steps to withdraw from the League. Manchuria would remain in Japanese hands until August of 1945, when it was liberated by Soviet forces.