Why is it that since the Tang Dynasty, all dynasties may not be Chang 'an?

Let's put it this way. First of all, why did the former dynasty build its capital in Chang 'an? It is because of his superior position in Chang 'an that strategically, he can co-ordinate the whole country.

why did you change the capital in the Tang dynasty? The reason is that the strength of the Tang Dynasty was greatly weakened, and the internal and external troubles were serious. In the Tang Dynasty, the system of our time was implemented, and many fan states were established, so that the national forces were scattered and centralized. Chang 'an, the capital, was not strong enough for the commander-in-chief of the whole country. With the gradual loss of control of fan states, the rise of ethnic minorities in the northwest posed a great threat to the Tang Dynasty. If Chang 'an continued to be its capital, it might always face a surprise attack from ethnic minorities in the northwest, so it was necessary to move the capital. At that time, the scene of the Tang Dynasty was like that of the Shang Dynasty, when the emperor was poor and the vassal was strong.

apart from historical reasons, there is also an important reason why Chang' an settled in Chang' an. That is, during the Sui and Tang Dynasties, the Silk Road, which started from Chang' an, made the world truly realize the importance of Chinese civilization. With the extreme development of the Tang Dynasty to the western regions, the peak of the Silk Road, Sui and Tang Dynasties continued to export culture to the west, and also absorbed some excellent cultures, such as papermaking. There was no gap between land civilizations, and it also affected neighboring countries.

The Turks in the northwest and the grassland empire represented by Uighur regarded the emperor of the Tang Dynasty as Tiankhan, and the ministries in the northeast surrendered to the Tang Dynasty. Japan and the Korean Peninsula in the east once worshipped Tang Wenhua in an attempt to imitate it, so there were Japanese Jian Zhen monks, which was also a great output of Chinese culture. With the decline of the empire, the shrinking of the empire's territory and the decline of the Silk Road, Chang 'an naturally withdrew from the historical stage, and gradually nomadic people played the leading role. Perhaps, because the Tang Dynasty was too prosperous, it became proud and indulged in the growth of ethnic minorities, which finally kicked off the demise of the Tang Dynasty and the birth of the Five Dynasties and Ten Countries.