Sometime in October, Ji Xing (吉興) surrendered the Yanbian Korean Autonomous Prefecture area and on 17 October, Yu Zhishan surrendered Eastern Liaoning to the Japanese. On 1 October, Zhang Haipeng surrendered the Taonan area. On 23 September, the Japanese took Jiaohe (Jilin Province) and Dunhua. On 21 September, the Japanese captured Jilin City. On 19 September, the Japanese occupied Yingkou, Liaoyang, Shenyang, Fushun, Dandong, Siping (Jilin Province), and Changchun. Likewise on 19 September, in response to General Honjō's request, the Joseon army in Korea under General Senjūrō 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. Under orders from Lieutenant General Jirō Tamon, troops of the 2nd Division moved up the rail line and captured virtually every city along its 1,170-kilometre (730-mile) length in a matter of days. However, Kwantung Army commander-in-chief General Shigeru Honjō instead ordered his forces to proceed to expand operations all along the South Manchuria Railway. On 18 September 1931 the Japanese Imperial General Headquarters, which had decided upon a policy of localizing the incident, communicated its decision to the Kwantung Army command. The Chinese–Japanese dispute in July 1931 known as the Wanpaoshan Incident was followed by the Mukden Incident. By the evening, the fighting was over, and the Japanese had occupied Mukden at the cost of five hundred Chinese lives and only two Japanese lives, thus starting the greater invasion of Manchuria. The Chinese troops were no match for the experienced Japanese troops. Zhang Xueliang's small air force was destroyed, and his soldiers fled their destroyed Beidaying barracks, as five hundred Japanese troops attacked the Chinese garrison of around seven thousand. On the morning of 19 September, two artillery pieces installed at the Mukden officers' club opened fire on the Chinese garrison nearby, in response to the alleged Chinese attack on the railway. In fact, a train from Changchun passed by the site on this damaged track without difficulty and arrived at Shenyang at 10:30 pm (22:30). However, the explosion was minor and only a 1.5-meter section on one side of the rail was damaged. At around 10:20 pm (22:20), 18 September, the explosives were detonated. The plan was executed when 1st Lieutenant Suemori Komoto of the Independent Garrison Unit (独立守備隊) of the 29th Infantry Regiment, which guarded the South Manchuria Railway, placed explosives near the tracks, but far enough away to do no real damage. Japanese soldiers of 29th Regiment on the Mukden West Gateīelieving that a conflict in Manchuria would be in the best interests of Japan, and acting in the spirit of the Japanese concept of gekokujō, Kwantung Army Colonel Seishirō Itagaki and Lieutenant Colonel Kanji Ishiwara independently devised a plan to provoke Japan into invading Manchuria by setting up a false flag incident for the pretext of invasion. The label of the invasion as ethically illegitimate prompted the Japanese government to withdraw from the League entirely.
With the invasion having attracted great international attention, the League of Nations produced the Lytton Commission (headed by British politician Victor Bulwer-Lytton) to evaluate the situation, with the organization delivering its findings in October 1932. The invasion, or the Marco Polo Bridge Incident of 7 July 1937, is sometimes cited as an alternative starting date for World War II, in contrast with the more commonly accepted one of September 1939. The US sanctions which prevented trade with the United States (which had occupied the Philippines around the same time) resulted in Japan furthering its expansion in the territory of China and Southeast Asia.
Japan's ongoing industrialization and militarization ensured their growing dependence on oil and metal imports from the US. The South Manchuria Railway Zone and the Korean Peninsula had been under the control of the Japanese Empire since the Russo-Japanese War of 1904–1905. Their occupation lasted until the success of the Soviet Union and Mongolia with the Manchurian Strategic Offensive Operation in mid-August 1945. At war's end in February 1932, the Japanese established the puppet state of Manchukuo. The Japanese invasion of Manchuria began on 18 September 1931, when the Kwantung Army of the Empire of Japan invaded Manchuria immediately following the Mukden Incident.