In an article on Korean-Chinese (Chaoxianren or Chaoxian minzu) in Korea, the so-called Chosun Ilbo newspaper of South Korea jingoistically proclaims that northeastern China during the 18th century was a part of Korea. LMAO! And more LMAO!
Firstly, refer to the map of Qing China below. Secondly, use some common sensical logic. The ancestral homeland of the Qing was Manchuria, which has always comprised the northeastern (dongbei) territories of China. (Manchus lived in Manchuria, for the benighted writers of the Choson Ilbo.)
At its apex, the Qing empire stretched from Outer Mongolia to Vietnam. An empire this large (and before 1842, quite powerful) surely could have afforded to protect and defend its own ancestral homeland from tiny Chosun (Chaoxian) Korea. In fact, Chosun (Chaoxian) Korea was a vassal/tributary state to Qing China. The Chosun (Chaoxian) king had to pay his respect to the Qing emperor every year or so by sending tributes to the Forbidden City.
Here is the offending paragraph from the Chosun Ilbo (July 6, 2011 online version):
Korean Chinese can trace their roots back to the late 18th century, at around the end of the Chosun Dynasty. At this time, Koreans began migrating in search of food to northeastern China, which was then considered a part of Korean territory.
Map of Qing China (Source: Wikipedia)