According to the conventional theory, the territory of Silla began in Gyeongju, Gyeongsang Province in the south of the Korean Peninsula and reached unified Silla, it is recognized the territory did not cross Pyongyang at all. This is based on the claim that the location of Andong Dohobu(安東都護府) established by Tang on the border of Silla is Pyongyang. It is said that all of them are present-day Pyongyang. This is based on the 'Hansagunjaepyongyang theory(漢 四郡在平壤設)' that both Pyongyang of Gojoseon and Nakrang-gun (樂浪 郡) established by Han(漢), which is being criticized in the academic world, are North Korea's Pyongyang. The problem of interpretation of the territory related to this is connected not only to Gojoseon and Goguryeo, but also to the territory of Unified Silla. However, looking at various historical sources in China, it is recorded that Andong Dohobu, which was established by the Tang Dynasty, and Pyongyang of Goguryeo are not presently Pyongyang in North Korea, but are recorded as 'Pyeongju Noryong-hyeon(平州 盧龍縣)' in Hebei Province, which is located in the Beijing area. It also matches the historical records. In addition, Tang called various kings of Silla 'Nakranggunwang (樂 浪郡王)'. Nakrang-gun(樂浪郡) is clearly recorded as Han(漢)'s land. In other words, it can be seen that the location of Nakrang-gun is deeply related to the border of unified Silla. And after the founding of Balhae(渤海), unified Silla and Balhae border each other, and it is recorded as 'Haeju(海州)' as it is located in the southern part of Namgyung(南京南海府), called 'Sillado(新羅道)' to Silla, and it is recorded as 'Haeju'. It was in the eastern part of the Nanha(灤河).
 As a result of studying the territory of Unified Silla through various historical documents and old maps, the western boundary between Unified Silla and Tang in its heyday occupied the territory up to the Nanha(灤河) in Hebei Province, and the territorial expansion of Balhae and the Yo(遼) After the founding of the country, the river area gradually shrunk to the east, and during the Goryeo(高麗) period, it moved to the current Yoha(遼河) area.