The so-called Western Dynasty and Eastern Dynasty are essentially based on the capital, so we can look at it more broadly and talk about the problem of "moving to the Eastern Capital" or "building the Eastern Capital" in ancient China, and here temporarily abandon the situation of the Western Jin Dynasty, the Eastern Jin Dynasty, the Southern Song Dynasty, and the Northern Song Dynasty, which was forced to move the capital due to the fall of the capital.
In ancient China, Luoyang was in the middle of the world, and the Kanto region where it was located was also the most culturally prosperous region, but the most powerful periods in Chinese dynasties, such as the Western Han Dynasty and the early Tang Dynasty, were all established in Chang'an, and the two were not diametrically opposed, the Eastern Han Dynasty followed the Western Han Dynasty but moved the capital to Luoyang, and Wu Zetian also moved the capital to Luoyang after the establishment of Wu Zhou, is there a connection between this?
Taking the Anshi Rebellion as the boundary, we can roughly divide the ancient Chinese history into two parts, we can see that before the Anshi Rebellion, there were many times when the capital was moved from Guanzhong to Guandong, or another eastern capital was built outside the Capital of Guanzhong, the more famous ones include the Zhou Gongyan construction of Luoyi, the Guangwu Emperor's move to the capital Luoyang, the Sui Emperor and Wu Zetian's relocation of the capital Luoyang, etc. We find that this phenomenon ran through the Western Zhou, Qin, Han, Sui and Tang Dynasties, so what is the reason behind it?
To explain this problem, we may wish to study a dynasty that did not move its capital, the Qin Dynasty. We can see from the Chu-Han War that the purpose of both Chen Sheng and King Huai was to restore the system of nations, not to replace the Qin Emperor with the Chu Emperor, so it can be said that the essence of the Chu-Han War was not only against the Qin State, but also against the Qin system, specifically the Qin-style Guanzhong military state system.
In short, the success of the Qin Dynasty stemmed from its establishment of a military system based on the geopolitical conditions and social customs of Guanzhong, which provided a strong mobilization force and achieved reunification, while its failure lay in the fact that after its reunification, it did not adopt a universal civil rule policy (the so-called universality is the political relationship between "one king and all the people" within the scope of "the world", and there is no tendency of a certain region), but continued the militarist policy of Guanzhong.
Is the historical lesson of the Qin Dynasty an isolated case? We can continue to examine the history of the Han Dynasty. Liu Bang neutralized the state in Han, and then also established the Three Qins, inheriting the territory of the Qin State during the Warring States period, and also inherited the political system of the Qin State, Han Xinshen Military Law and Xiao He Ding Household Registration laid the foundation for the Han Dynasty to establish the Guanzhong military state system, and the subsequent Five-Year Edict of Emperor Gao directly proved that the Han Dynasty completely inherited the military merit system of the Qin Dynasty, so it can be said that the Han Dynasty in the Chu and Han Dynasties was the successor of the Qin Dynasty.
However, the history after the two is completely different, the Han Dynasty first implemented the Huang-Lao policy to alleviate social contradictions, gradually cleaned up the power of the princes, and then in the period of Emperor Wu, confucianism was exclusively respected, and reached an agreement with the Culture of Kwantung, and then pushed to the whole country, truly realizing the integration of the whole society, so the entire Early Han Dynasty was a process from the Guanzhong military system to the universal imperial system.
At the beginning of the founding of the Western Han Dynasty, Liu Jing said to Liu Bang that Luoyang was "for the sake of the world... Without virtue, it is easy to perish], so it is suggested that Liu Bang build the capital Chang'an, and limit the princely states by virtue of the natural danger of Guanzhong, reflecting that the opposition between Guanzhong and Guandong in the early Western Han Dynasty was still profound, and the guanzhong standard still occupied the mainstream. After nearly a hundred years of melting, the cultural contradictions between Guanzhong and Kanto have gradually weakened, the concept of the Seven Kingdoms has long been replaced by states and counties, and Luoyang, which has moved the capital to "you have virtue and is easy to be king", has been put on the agenda.
The proposal to move the capital to Luoyang first began during the reign of Emperor Yuan of the Western Han Dynasty, and the Book of Han in the Book of Yifeng contains the following book: "Your Majesty wishes to move the capital to Chengzhou ... After long live, he grew up to be Emperor Gaozong. When Wang Mang was in power, the wind of moving the capital to Luoyang rose again, that is, what Wei Wei said: "DingDi De, the state of Luoyang." During the reign of Emperor Guangwu, the capital was finally moved, which also meant that China was officially transformed from a militaristic state in Guanzhong to a universal empire.
The above historical process was first established by the Duke of Zhou. The Zhou people were based in the West and eventually cut the Merchants to establish the Zhou, but the customs in Guanzhong were very different from those in the Kanto Region, and the rule of the Zhou people could not be implemented, and the establishment of the state soon led to the Wu Geng Rebellion. After the rebellion of Zhou Pingding, in order to implement the rule over the Kwantung, he built the eastern capital Luoyi, gradually shifted the political center to the east, and ruled the four sides in the world.
The third repetition of this process occurred during the Sui and Tang dynasties. After three hundred years of turmoil in the Southern and Northern Dynasties of the Wei and Jin Dynasties, history once again returned to Guanzhong, and Yuwen Taijiu joined forces with the Forces of Northern Town and the Guanlong Hao Clan to form a Guanlong military state system with the prefectural military system as the core, which was reunified by Emperor Wen of Sui in less than a hundred years. For the empire, an important proposition is how to get rid of the influence of the Guanlong clique and become a universal empire. In order to achieve this goal, the Sui Emperor moved the capital to Luoyang, promoted the Jiangnan and Shandong Shi clans, and tried to suppress the political power of the Guanlong clique, which eventually caused dissatisfaction among the Guanlong clique represented by Yang Xuangan, and eventually led to the demise of the Sui Dynasty.
The unification of the Tang Dynasty meant the re-realization of social integration, after more than a hundred years of war, the Guanlong clique gradually withered, Tang Taizong re-established the "Clan History" to represent the reconciliation of Guanzhong and Kanto, the process of universalization of the empire has since been determined, and the last blow to the aging Guanlong clique is the Wuhou from Shandong. After Wu Zetian established Wu Zhou, he was anxious to get rid of the old forces in the dynasty, so he moved the capital to Luoyang and dealt a fatal blow to the Guanlong clique.
All in all, due to its special geographical conditions and social customs, Guanzhong is easy to form a militaristic system with strong mobilization power, and it is easy to achieve reunification, but it cannot be ruled immediately by winning the world immediately, and the profound opposition between Guanzhong and Kanto culture makes it difficult to implement Guanzhong's military policy in Kanto, so moving from Guanzhong to universalization has become a necessary proposition in the Han and Tang Dynasties, and moving the capital Luoyang often represents the final completion of this process. In short, the frequent relocation of capitals from the west to the east is because the West is easy to get the world, and the East is suitable for ruling the world.
However, it must be pointed out here that the two are not completely consistent, the relationship is very complicated, the two Han dynasties finally moved the capital to Luoyang during the Guangwu period, but its universalization process was basically completed in the era of Wu Zhaoxuan, and the return of the capital to Chang'an after the death of Wu Hou did not mean the resurgence of Guanlong's forces, and the political factors were equally complex. This process did not recur after the Tang Dynasty, and I think there are probably two reasons, one is the further weakening of the Guanzhong region during the Five Dynasties period, and the other is that China's political system was further improved at the time of the Tang and Song Dynasties, and the regional-based policy could not be reproduced.
Finally, back to the original topic, most of China's most powerful eras were established in Chang'an, probably because its military system had not yet collapsed, and its mobilization power was still strong, while the lack of martial arts in the Luoyang era was closely related to its policy towards civil rule.
bibliography:
Chen Suzhen: Spring and Autumn and the Han Dynasty
Michio Tanigawa: A History of the Formation of the Sui and Tang Empires
Li Kaiyuan: The Establishment of the Han Empire
Chen Yinke: Treatise on the Political History of the Tang Dynasty