Liu Bang once asked his subordinates about building the capital, because he also chose Luoyang, but his subordinates Lou Jing and Sean suggested that he build the capital in Guanzhong. Later, Liu Xiu, Emperor Guangwu of Han Dynasty, revived the Han Dynasty, where Chang 'an was located, and a lot of materials needed to be brought in from other places. In order to reduce people's material transportation labor, Chang 'an was not built as the capital, but Luoyang was built as the capital, because Luoyang is located in the world and has a good geographical position, which is conducive to the transportation of materials and social production has not been particularly damaged.
Chang 'an in Sui and Tang Dynasties was different from Chang 'an in Han Dynasty. Chang 'an in Sui and Tang Dynasties was a new capital established by Emperor Wen in the southeast of the former Chang 'an, which was famous for its prosperity. Later, Li Yuan proclaimed himself emperor to build the Tang Dynasty and changed Daxing City to Chang 'an. After several expansions, the perimeter has reached 35.56 kilometers and the area is about 84 square kilometers, which is 9.7 times that of Xi 'an City Wall, 2.4 times that of Chang 'an City in Han Dynasty and 64 times that of Luoyang City in Northern Wei Dynasty. It is 1.8 times that of Luoyang in Sui and Tang Dynasties, 1.7 times that of Dadu in Yuan Dynasty, 1.9 times that of Nanjing in Ming Dynasty, 1.4 times that of Beijing in Ming and Qing Dynasties, 7 times that of Constantinople in 447 AD, 6.2 times that of Baghdad in 800 AD and 7 times that of ancient Rome. In the prosperous Tang Dynasty, Chang 'an was the largest and most prosperous international city at that time.
Luoyang is no longer the real capital. Most dynasties regarded it as the capital, not the political center, because there are many plains near Luoyang, and there is no natural barrier to rely on. Different from Guanzhong, Ma Pingchuan enjoys convenient transportation and developed commerce. Geographical location in the world, as long as it is the capital or economic center.
In history, the capital of Nanjing was the Sun Wu regime in the Three Kingdoms period, and the Song Qi Liang Chen in the Western Jin Dynasty and the Southern and Northern Dynasties. Together, it was the Six Dynasties. This is the origin of Nanjing, the ancient capital of the Six Dynasties. Later, Zhu Yuanzhang proclaimed himself emperor in Yingtian, Nanjing, and made his capital. However, it is said that the place where Zhu Yuanzhang really wants to build the capital is Gu Chang 'an. He sent Prince Zhu Biao to inspect Guanzhong, but the short-lived prince died the next year. Zhu Yuanzhang's white-haired people sent black-haired people, and when he was getting older, he moved the capital on hold. It can be said that Nanjing, as the capital, especially during the Three Kingdoms, the Jin Dynasty and the Southern and Northern Dynasties, was mainly because most of these countries were located in the southwest, while Nanjing, as an ancient city built during the Warring States period (the so-called "King of Chu and Qin"), became the first choice, but its terrain was not dangerous, and the south was also dominated by economic development throughout the history of the Chinese nation, so it was impossible to control the four seas and reject the northern Hu like the Central Plains.
The history of Beijing as the capital can't be compared with the past. Historically, Zhao Gong of the Zhou Dynasty was the first person to build Beijing as its capital. Later, it was not until Jurchen established the Jin Dynasty that Beijing was designated as Zhongdu. Yuan Dynasty became the national political center, renamed Dadu. Later, Judy, the prince of Yan, successfully seized the throne of Emperor Jianwen, because his fief was in Beiping, which was the original capital of the Yuan Dynasty, and Judy, the Ming emperor, moved to Beijing in order to strengthen the border defense in the north and safeguard the security in the north, in order to defend the country for the emperor (almost every Ming emperor followed this creed except the small court in Nanming, including Emperor Chongzhen who hanged Jingshan Park).
The reasons why each dynasty made its capital are different, but most of them are also because of the geographical location of the country, whether it is a unified dynasty, and whether the local terrain is dangerous.