The Chinese-Japanese dispute in July 1931 (the Wanpaoshan Incident) was followed by the Mukden Incident, on September 18, 1931. The same day as the Mukden Incident, the Japanese Imperial General Headquarters, which had decided upon a policy of localizing the incident, communicated its decision to the Kwantung Army command. However, Kwantung Army commander-in-chief General Shigeru Honjō instead ordered his forces to proceed to expand operations all along the South Manchurian Railway. Under orders from Lieutenant General Jirō Tamon, troops of the 2nd Division moved up the rail line and captured virtually every city along its 730-mile length in a matter of days, occupying Anshan, Haicheng, Kaiyuan, Tiehling, Fushun, Szeping-chieh, Changchun, Kuanchengtzu, Yingkou, Antung, and Penhsihu.
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Likewise on September 19, in response to General Honjō's request, the Joseon army in Korea under General Senjuro Hayashi ordered the 20th Infantry Division to split its force, forming the 39th Mixed Brigade, which departed on that day for Manchuria without authorization from the Emperor.
Between September 20 and September 25, Japanese forces took Hsiungyueh, Changtu, Liaoyang, Tungliao, Tiaonan, Kirin, Chiaoho, Huangkutun and Hsin-min. This effectively secured control of Liaoning and Kirin provinces and the main line of rail communications to Korea.
Tokyo was shocked by the news of the Army acting without orders from the central government. The Japanese civilian government was thrown into disarray by this act of "gekokujo" insubordination, but as reports of one quick victory after another began to arrive, it felt powerless to oppose the Army, and its decision was to immediately send three more infantry divisions from Japan, beginning with the 14th Mixed Brigade of the IJA 7th Division.
During this era, the elected government could be held hostage by the Army and Navy, since Army and Navy members were constitutionally necessary for the formation of cabinets. Without their support, the government would collapse.