China proper, also called Inner China are terms used primarily in the West in reference to the traditional "core" regions of China centered in the southeast. The term was first used by Westerners during the Manchu-led Qing dynasty to describe the distinction between the historical "Han lands" (漢地)—i.e. regions long dominated by the majority Han population—and the "frontier" regions of China where more non-Han ethnic groups and new foreign immigrants reside, sometimes known as "Outer China". There is no fixed extent for China proper, as many administrative, cultural, and linguistic shifts have occurred in Chinese history. One definition refers to the original area of Chinese civilization, the Central Plain ; another to the Eighteen Provinces of the Qing dynasty. There was no direct translation for "China proper" in the Chinese language at the time due to differences in terminology used by the Qing to refer to the regions. Even to today, the expression is controversial among scholars, particularly in mainland China, due to issues pertaining to contemporary territorial claim and ethnic politics.

The Empire of Japan's Kwantung Army invaded the Manchuria region of the Republic of China 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.