The Qing identified all their territories as China

Some people have a mistaken conception that the Qing and Manchu did not identify their entire empire as Zhongguo 中國 (China), and only referred to Han inhabited provinces as Zhongguo (the so called "China proper") while governing other parts as "Manchuria", "Mongolia", "Tibet".

That is blatantly false. The early Qing Emperors from Shunzhi, Kangxi, Yongzheng, and Qianlong identified the entire Qing Empire as Zhongguo.

It was Han Ming loyalists, not the Qing or Manchu, which tried to resist identifying non-Han territories like Mongolia as part of Zhongguo.

The Qing Emperors even invented a new Manchu term to correspond with Zhongguo- "Dulimbai Gurun". Dulimba means "middle" in Manchu, like 中 Zhong means "Middle", and Gurun means "state" or "Kingdom" in Manchu like 國 Guo means state or kingdom.

The Qing declared that all parts of the Qing Empire were Zhongguo 中國, including Mongolia, Tibet, Xinjiang, and Northeast China (Manchuria). When Han advisors to the Qing Emperors tried rejecting that idea and claimed Zhongguo only referred to Han areas, the Qing emperor openly rebuked them and said that  Zhongguo 中國 referred to non-Han areas of the Qing as well.

In the Treaty of Nerchinsk with Russia, the Manchu language version of the treaty said that the lands south of the Argun river in Manchuria belonged to "Dulimbai Gurun" (China). In the Treaty of Kyakhta signed with Russia, the Manchu language version of the treaty referred to the Outer Mongolian territory of the Qing Empire as "Dulimbai Gurun" (China), referring to the Qing subjects in that area as "dulimbai gurun i niyalma" (中國人) "Chinese people". In the Manchu Tulišen's travelogue on his journey to the Oirat Mongols on the Volga in Russia, he referred to the Qing as "Dulimbai Gurun".

The Kangxi and Qianlong Emperors repeatedly referred to lands in Manchuria at the Korean border as belonging to Zhongguo (China).

When the Manchu Bannermen conquered Dzungaria (in northern Xinjiang) from the Oirat Mongol Dzungar Khanate, they sent a Manchu language memorial boasting that the land of  Dzungaria was now absorbed into "Dulimbai Gurun".

New Qing Imperial History: The Making of Inner Asian Empire at Qing Chengde - Ruth W. Dunnell, Mark C. Elliott, Philippe Foret, James A Millward - Google Books

Number 19

The Manchu Way: The Eight Banners and Ethnic Identity in Late Imperial China - Mark C. Elliott - Google Books

Manchu language version at number 44

New Qing Imperial History: The Making of Inner Asian Empire at Qing Chengde - Ruth W. Dunnell, Mark C. Elliott, Philippe Foret, James A Millward - Google Books

Some Han advisors to Qianlong tried rejecting Qianlong's annexation of Dzungaria and the rest of xinjiang, saying that they were not part of Zhongguo, but Qianlong rebuked them and said that they were part of 中國. Some Han Ming loyalists tried to avoid referring to non-Han areas as China just because they opposed the Qing. This is the exact opposite of the false notion that its Han nationalists who tried identifying Qing as China to gain more territory, while in reality its the Qing and Manchu themselves who did this since 1644.

This article quoted directly from Manchu and Chinese language Qing official documents, all of which I mentioned above, which identify all areas of the Qing Empire as 中國/Dulimbai Gurun/China.
 
https://web.archive.org/web/20140325231543/https://webspace.utexas.edu/hl4958/perspectives/Zhao%20-%20reinventing%20china.pdf

The article is availible in jstor

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Reinventing China

As you can see in this Manchu-German dictionary, Dulimbai Gurun is a direct equivalent of 中國.

Handwörterbuch der Mandschusprache - Erich Hauer - Google Books


"Manchuria" as a place name/geographic name, is a Japanese invented concept. The Qing and Manchus never referred to their homeland in Jilin and Heilongjiang as "Manchuria". The area was called "Nurgan" 奴兒干during the Ming dynasty, and during the Qing, Manchus referred to it as "san dong sheng" 三東省 (Three eastern provinces). The name 满洲 Mǎnzhōu (Manju) was only used to refer to the ethnic group.

A Japanese mapmaker took the name 满洲 (Manshū in Japanese) and put it on a map to refer to the region where Manchus came from. A westerner copied this map and brought it to Europe, and this is how the name "Manchuria" was born to refer to the geographic area.

Westerners noted how the Manchus themselves did not refer to the area as Manchuria.

China and the Manchus - Herbert A. Giles - Google Books

Tumen Jalafun Jecen Aku: Manchu Studies in Honour of Giovanni Stary - Google Books

Tumen Jalafun Jecen Aku: Manchu Studies in Honour of Giovanni Stary - Google Books

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The Russo-Japanese War in Global Perspective: World War Zero - Google Books

Japan at the Millennium: Joining Past and Future - Google Books

Chang Tso-lin in Northeast China, 1911-1928: China, Japan, and the ... - Gavan McCormack - Google Books

Intoxicating Manchuria: Alcohol, Opium, and Culture in China's Northeast - Norman Smith - Google Books

American Diplomacy Concerning Manchuria - Chao-ying P»an - Google Books

https://dlib.lib.washington.edu/researchworks/bitstream/handle/1773/20679/Garcia_washington_0250E_10365.pdf?sequence=1

The Making of a Chinese City: History and Historiography in Harbin - Søren Clausen - Google Books