When was the territory of Korea set by the Tang Dynasty lost?

The Book of Old Tang Dynasty records that in September of the first year of Tongzhang (AD 668), Li Ji pacified Korea. Korea was originally divided into five parts, * * * 176 cities with a population of 697,000. In that year1February, the Tang Dynasty divided North Korea into 9 counties and 42 states 100 county, and set up Anton Khufu in Pyongyang, the former capital of North Korea, for unified management.

The management mode of the Tang Dynasty adopted the detention system, that is, under the condition of not changing the ruling mode of North Korea, the original leader of North Korea was still appointed as the chief of the governor's office, the state secretariat and the county magistrate, leaving only 20 thousand Tang soldiers headed by General Xue to guard Pyongyang, that is, Anton House.

South Korea has a long way to go, backward economy and poor roads. In addition, due to the detention system, no population migrated to North Korea, and Silla was gradually eroded, including Baekje, and many lands of Anduhufu gradually fell into Silla's hands. The Tang Dynasty did not take measures. But began to give up these lands.

In February of the third year of Shangyuan (AD 676), the Tang Dynasty took the initiative to move Anton House to the old town of Liaodong County (now northeast Anshan) for resettlement. In the second year, in the second year of Yifeng (AD 677), the Tang Dynasty once again moved to the new town of Liaodong County in the north and east.

By June of the first year of the reign of Wu Zetian (AD 698), the land of the viceroy of Anton had been eroded so much that it was no longer possible to maintain the scale of the viceroy, so it was downgraded to the viceroy of Anton. Although in the first year of Shenlong (A.D. 705), it was re-upgraded to Andong Hufu. But the land is still losing. In the second year of Kaiyuan (AD 7 14), Andong Hufu moved further westward and settled in Pingzhou (now Lulong, Hebei Province), which meant that Andong Hufu moved out of its own jurisdiction. Although in the second year of Tianbao (AD 743), Anton Khufu once again moved eastward to the old county town in western Liaoning. But in 755 AD, An Shi Rebellion broke out. Anton Khufu is behind the rebels. Then came the separatist regime. During the German period (July 756-February 758), this land was abandoned, and the institutional setup was also abandoned.