The Empire of Japan's Kwantung Army invaded Manchuria on 18 September 1931, immediately following the Mukden Incident. At the war's end in February 1932, the Japanese established the puppet state of Manchukuo. Their occupation lasted until the success of the Soviet Union and Mongolia with the Manchurian Strategic Offensive Operation in mid-August 1945, towards the end of the Second World War.

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. Japan's ongoing industrialization and militarization ensured their growing dependence on oil and metal imports from the US. 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. The invasion of Manchuria, or the Marco Polo Bridge Incident of 7 July 1937, are sometimes cited as an alternative starting dates for World War II, in contrast with the more commonly accepted date of September 1, 1939.