Wikipedia
Manchukuo was a puppet state in Northeast China and Inner Mongolia, which was governed under a form of constitutional monarchy. The area, collectively known as Manchuria by westerners and Japanese, was designated by China's erstwhile Qing Dynasty as the "homeland" of the ruling family's ethnic group, the Manchus, but the Manchus themselves never used "Manchuria" (滿洲) as a place name to refer to the area. In 1931, the region was seized by Japan following the Mukden Incident and a pro-Japanese government was installed one year later with Puyi, the last Qing emperor, as the nominal regent and emperor. Manchukuo's government was abolished in 1945 after the defeat of Imperial Japan at the end of World War II. The territories formally claimed by the puppet state were first seized in the Soviet invasion of Manchuria in August 1945, and then formally transferred to Chinese administration in the following year.
Manchus formed a minority in Manchukuo, whose largest ethnic group were Han Chinese. The population of Koreans increased during the Manchukuo period, and there were also Japanese, Mongols, White Russians and other minorities. The Mongol regions of western Manchukuo were ruled under a slightly different system in acknowledgement of the Mongolian traditions there. The southern part of the Liaodong Peninsula was ruled by Japan as the Kwantung Leased Territory.