In 696, Khitan started attacking Tang Dynasty and once defeated 170,000 Tang Dynasty soldiers. The Khitan uprising played a huge role in upheaval of Tang Dynasty in northeast. During this period, Khitans occupied Liaoxi Corridor, cutting off link between Tang and Liaodong dynasties. Fortunately, Turks attacked Khitan from behind, causing Khitans to temporarily retreat, and then Tang dynasty briefly regained control of Liaodong.
After fall of Khitans, it was annexed to Turks, but so far it will not pose a threat to Tang dynasty. But there's a big threat coming, and that's Mohe. Mohe is predecessor of Jurchen tribe, which is divided into Heishui Mohe and Sumo Mohe. During reign of Wu Zetian, Da Zuorong, leader of sumo tribe, migrated to Songhua River region and founded Zhen Guo. According to historical records, in 697, Da Zuorong defeated army of Tang Dynasty at Battle of Tianmenling.
Map of Tang dynasty in middle of Tang era
Since then, Andong Protectorate of Tang Dynasty has faced enemies from all sides, and surrounding Goguryeo, Mohe, Shiwei, Khitans and Turks look at each other. After Tang Xuanzong came to power, he decided to change this situation. There are three main measures.
(1) Move capital Khufu inland. In 714, Anton Duhufu moved to Yingzhou (Chaoyang) in Liaoxi corridor, and in 742 to Gujuncheng (Jinzhou Yixian).
(2) Establish three towns of Pinglu, Fanyang, and Hedong and deploy heavy troops to keep Turks and Khitans from going south. We all know result. In 755, Zedu's envoy An Lushan launched "Anshi Rebellion" and Tang dynasty went from prosperous to decline. By 761 Anton's governor's estate was abolished.
(3) Actively maintain diplomatic relations with various ethnic groups in Northeast China by designating Zhen Guo Bohai Governor's Mansion (later canonized as Bohai State) and Heishui Mohe Governor's Mansion Heishui, Shiwei is canonized as Shiwei Governor's Mansion. We should not understand these three capitals as territories, Tang Dynasty has no control over them, not even a sphere of influence.
An overview of situation in Northeast China during Tang Dynasty
According to above content, it can be seen that Tang Dynasty lost control of northeast during Anshi Rebellion. During Anshin uprising, mansion of Governor Anton, which existed only nominally, was officially abolished. After Anshi rebellion, vassal cities in Hebei region expanded to form "Three Cities in Hebei". The Tang Dynasty could not even control "Three Cities in Hebei", let alone control Liaodong, and it is even more absurd for Tang Qixiang to paint a picture of end of Tang Dynasty in Heilongjiang.
Tang version of map of end of Tang dynasty
So, after Tang forces left Liaodong, who took over? Du Yu (735–812), prime minister of Tang Dynasty, once said, "Andong Mansion... is now known as Dongyi Land." That is, Anton's mansion in past is now occupied by Dongyi. Where is Dongy? Du Yu also said, "Gao Zongping Goryeo and Baekje traveled over a thousand miles in Haidong, but were captured by Silla and Mohe and lost." According to records of Cefu Yuanggui, in fifteenth year of Kaiyuan's reign, Tang Dynasty canonized Prince Suwei in Bohai, Dachangbo as "Founder of Xiangping County" and was recognized by Tang Dynasty.
Some historical books also record historical fact that Bohai owns Liaodong. For example, in Japanese history book "Continued Japanese Post-Ji Vol. 10", a copy of Bohai Zhongtai provincial document contains phrase "Japan is far from east, and Liaoyang is blocked from west." And "Cizhi Tongjian" is an unshakable iron proof. Among them " The late Tang Ji" reports that during Five Dynasties "all barbarians in northeast belonged to Khitans, but Bohai did not accept this; attack Liaodong in Bohai Sea", and his Chronicle of Khitan Kingdom also records that "Tokyo (Liaoyang) is old site of Bohai Sea, and it was obtained after more than 20 years of Abaoji's reign . battle". The History of Liao also records: "Liaoyang, Liaodong of Han Dynasty, is hometown of Bohai Sea; ... Tokyo, originally Bohai Sea, built Nanjing on its land" The Bohai State not only occupied Liaodong, but also accepted Liaoyang as Nanjing.
Summarizing, Tang Dynasty began to withdraw from Liaodong during Kaiyuan period of Tang Xuanzong's reign and completely relinquished control of Liaoxi after Anshi rebellion. Thus, Tang Dynasty's jurisdiction and control over Northeast came to an end. Bohai Kingdom, which succeeded Tang Dynasty under Liaodong, after which Liaoyang became Bohai Kingdom's Nanjing. As for Tang Qixian's portrayal of last years of Tang Dynasty before Heilongjiang, and even breaking through Waixingan Mountains without a hat, this is a serious mistake and we cannot believe it.