Sixteen Prefectures

The Sixteen Prefectures, more precisely known as the Sixteen Prefectures of Yan-Yun (traditional Chinese: 燕雲十六州; simplified Chinese: 燕云十六州; pinyin: Yānyún Shíliù Zhōu) or the Sixteen Prefectures of You-Ji (Chinese: 幽薊十六州; pinyin: Yōujì Shíliù Zhōu), were a historical region in North China that comprises present-day municipalities of Beijing, Tianjin and parts of northern Hebei and Shanxi provinces north of the Hai River and its two northern tributaries Sanggan and Juma River. The region's name came from the sixteen military district prefectures (zhou) of Tang dynasty's northeastern borderlands under the fanzhen administration of the Youzhou and Hedong jiedushi, whose seats were at the Yan Prefecture and Yun Prefecture, respectively.

Situated around the Great Wall within the Yan Mountains and the Heng Mountain, the Sixteen Prefectures were a strategically important gateway region into the Central Plains and shielded the North China Plain from Hu incursions from the northeast, north and northwest, reinforced by riverine logistic transport of the Grand Canal. During the chaotic Five Dynasties and Ten Kingdoms period after Tang dynasty's collapse, the region was ceded to the Khitans in 938 AD by Later Jin founder Shi Jingtang, who desperately sought Khitan aid in his selfish rebellion against his brother-in-law, Emperor Li Congke of Later Tang. This act of treason subsequently caused the various Chinese states and dynasties to the region's south (including the Later Jin itself) to become vulnerable against invaders from the north (who used the region as a strategic staging area), as there were no longer any significant natural barriers north of the Yellow River capable of halting large-scale cavalry incursions. The region was marred by constant military conflicts for the next three centuries, both by southern Chinese regimes (such as the Later Zhou and the Northern Song dynasty) attempting to recapture the region and by new northern invaders (such as the Jurchens and later the Mongols) against the old occupiers (the Liao dynasty and the Jin dynasty, respectively), until the Mongol Empire conquered northern China in 1234 AD. The region was not recovered back into Han Chinese control until four centuries after its loss, when the Ming dynasty's successful northern expeditions overthrew the Mongol Yuan dynasty and captured the capital Dadu (modern-day Beijing) in 1368 AD.