Conditions for China to be proclaimed emperor in ancient times

A country has only one regime and only recognizes one. For example, in the Northern Song Dynasty and the Southern Song Dynasty, there was the Great Khan State, the predecessor of Xixia, Liao, Jin and Yuan Dynasties, but the whole country only recognized the two Song regimes as legal rulers. Otherwise, why don't the others call themselves emperors and call themselves kings (Xixia)? Even if the other three have emperors, they are only confined to the area under his jurisdiction. After that, he had no right to interfere, but the Song regime did not have this restriction, that is, their strength (especially in the Southern Song Dynasty) was not very strong, so they did not make those small border countries bow to chenchen like the Sui and Tang Dynasties.

As for the two analogies you made: the first analogy, you regard those small local governments like vassal States as the ones that rule the whole country. This is obviously a wrong view and view, because you have forgotten the saying that the brave in the Central Plains win! During the period of Three Emperors and Five Emperors, whoever enters the Central Plains first will be the overlord of the Central Plains, and who will have the right to rule this vast land! And therefore derived a word called the Central Plains Dynasty! Do you think that the example I talked about before, if you changed the Great Khan State into Kublai Khan of the Yuan Dynasty according to your idea, you wouldn't have to go to so much trouble to annex Xixia and Jin State and then destroy the Southern Song Dynasty, enter the Central Plains and unify the mess left by the Song Dynasty! The first emperor, Qin Shihuang, changed from being king to being emperor, so he didn't have to spend so much energy, money, manpower and time to destroy the six countries and unify the Central Plains. It is better to keep the status of princes and monarchs unchanged, and Emperor Wendi of Sui Dynasty, the founding emperor of Sui Dynasty, would not have to break the long-term pattern that the Northern and Southern Dynasties unified the whole country after the Three Kingdoms and the Jin Dynasty! You should reread your history. Historically, Ying Zheng, Emperor Wendi of Sui Dynasty and Kublai Khan of Yuan Shizu were all kings who unified and split the country. In addition to them, there was Song Taizu Zhao Kuangyin, the founding emperor of the Northern Song Dynasty, who unified the Five Dynasties and Ten Kingdoms produced at the end of Li Tang and established a powerful new dynasty. This dynasty was much stronger than the Southern Song Dynasty, but not as good as the Sui and Tang Dynasties. The second example is the western practice. The imperial system they practiced is different from that of our ancient dynasty rulers in appearance and culture, and there is nothing to talk about because of their different national conditions. Moreover, most of them are under their jurisdiction not only in the country where they live, but also in other lands on different continents. Otherwise, it is a colonial country. Unless the king of their country holds a coronation ceremony, their rights are limited to that acre of land. Britain, for example, is a British empire composed of three islands: England, Northern Ireland and Scotland, but the land that does not belong to those three islands, such as India, Australia and New Zealand, also belongs to it. Don't you know? These countries all have a governor, who is the symbolic leader of these countries, although he has no real power. Their appointment and removal is decided by the British government or the royal family!