In 1931, Japan invaded Manchuria in order to expand their Empire and gain control of China's natural resources, but also ostensibly to restore order to a China embroiled in a struggle between Nationalists and Communists, and to attract trade back to the region. After the invasion, Manchuria was reorganised into the puppet state of Manchukuo, ruled by the ousted Chinese Emperor Pu Yi. The Kwantung Army occupied the region and Kwantung Army Intelligence established itself at Hsinking. Chinese people continued to refer to the region as Manchuria. (PROSE: The Shadow of Weng-Chiang)
Peasants in Manchukuo were subjugated by the Kwantung Army and forced to work on the construction of Zhong Ma fortress, where Japanese military scientists sought to develop biological weapons. The Seventh Doctor and Edward Grainger travelled to the region in 1933 to rescue Mai Ling from the fortress (PROSE: Log 384)
Disputes over the province continued deeper into the 1930s. (PROSE: The Year of Intelligent Tigers) The Kodo Ha and Tosei Ha factions of the Imperial Japanese Army both favoured further expansion in Manchukuo, the former to offset strategic advantages enjoyed by the Soviet Union. They got their way by forcing the latter's hand by sparking an incident at Marco Polo Bridge.
When the Pacific War began in Asia in July 1937, the front lines opened up in Manchukuo, with the Japanese Twelfth Army pushing south into Shangdong, although their immediate aim was further consolidation of Manchuria. (PROSE: The Shadow of Weng-Chiang)
Towns and villages in Manchuria suffered from Japanese chemical attacks from germ-ridden packages developed in Zhong Ma Fortress and Unit 731, which were dropped throughout the region until the end of World War II. (PROSE: Log 384)