In the Ming Dynasty, Yanbian was governed by the Jianzhou Guard-district, and in the late Qing Dynasty the area was divided into the Yanji and Hunchun sub-prefectures. From 1644 to the 1800s the Manchurian administrators of the Qing state attempted to separate northeast China, politically and ethnographically, into a "Manchuria" to which they could retreat in case an ethnically Han Chinese dynasty regained control over China. In the 19th century, Korean immigrants migrated en masse from the Korean peninsula to China. After the foundation of the Republic of China, a second wave arrived. The population increase was caused by the Japanese invasion of that region. After the end of World War II, many Koreans did not go back to Korea. Instead, they joined the Chinese Civil War. When the civil war was over, the new Chinese government gave Koreans their own autonomous region in 1952. Yanbian was upgraded to an ethnic autonomous prefecture in 1955.