The grasslands north of the Great Wall and the Central Plains have very different systems. Rainfall in the grasslands is insufficient, and people can only live on nomadic herding. This made it impossible for the steppe to establish a huge ** financial system like the Central Plains Empire. The state collects taxes and feeds through taxes; However, there is a premise that the cost of collecting taxes must be less than the cost of taxation, which can only be achieved if the population is settled and can be organized into households. Nomads live in pursuit of water and grass, and are highly mobile, and it is too easy to evade taxes, and the cost of collecting taxes must be greater than their taxes. Therefore, it is impossible to establish a ** financial system on the steppe. Before Qin unified the world, there was no strong unified grassland people, and the historical accounts were used by the Central Plains vassal states to confront other Central Plains vassal states, such as the Zhou Youwang "Beacon Fire Opera Princes", the dog Rong was the object of Shenhou's use, and with the help of the strength of the dog Rong eliminated the Western Zhou. After the unification of Qin, Meng Tian attacked northward, causing the Xiongnu to retreat more than 700 miles and recover the Hetao area. But by the time of the Western Han Empire, a powerful Xiongnu empire seemed to fall from the sky and towered in the north. So how did this powerful Xiongnu empire come into being?
The most fundamental reason for the emergence of the steppe nomadic empire was the unification of the Central Plains into a huge agricultural empire. The resources on the grasslands are limited, and except for a few products such as meat and milk, the survival resources needed by nomadic herders must be obtained from the agricultural areas of the south. There are usually two ways to get it, war and **, which are the cheaper ways. But the question is whether the Central Plains is willing to engage with the steppes**? When the Central Plains is not unified, the vassal states of the Central Plains will conduct ** with the grassland tribes, and buy important war materials and horses from the grassland, while the vassal states that do not carry out ** with the grassland will be in a disadvantageous situation in the war with other vassal states. Therefore, the princes of the Central Plains are inevitably related to the struggle for hegemony and the dispersion of the grasslands. The Central Plains countries and different tribes in the grassland do different transactions, the Central Plains can not form a unified market, for many small tribes on the grassland, this kind of ** does not need to rely on the alliance with the large tribes, but also can live and survive in the trade with the vassal states of the Central Plains. 
But once the Central Plains are unified, the Central Plains Empire can use political means to close **, or stipulate the increase of **Central Plains products**. Once faced with this situation, for many small tribes on the grassland, they could not survive alone, and they could only unite to form a large tribal alliance to fight wars and ** in order to survive in the harsh environment of the East Asian grasslands, so a powerful nomadic empire appeared. 
The population of the combined steppe empire is still far less than that of the Central Plains Empire, but its combat effectiveness is generally stronger than that of the Central Plains Empire. The reason is that, on the one hand, the steppe army is dominated by cavalry, which has a mobility far beyond that of the Central Plains army. On the other hand, production, life, and fighting on the grassland are completely together, and their combat efficiency is high and the logistical pressure is low, which is far from being comparable to the Central Plains army. In addition, the grassland is poorer than the Central Plains, for the Grassland Empire, the war is almost a net gain, for the Central Plains Empire, the war is a negative return, requiring strong logistical support, and the war benefits and desires on both sides are very different, so that the Grassland Empire will pose huge military pressure on the Central Plains Empire. 
The Prairie Empire was strictly a tribal confederation. Due to the special environment of the grassland, it was impossible to form a tax system like the Central Plains, and the Great Khan of the alliance could only control the distribution of the spoils of war looted from the Central Plains to control the alliances of the various tribes in the empire. Therefore, the small tribes are only nominally loyal to the Great Khan, and have autonomy in their respective tribes, once the Great Khan loses in the war against the Central Plains Dynasty, the tribal alliance will collapse, for example, the Xiongnu lost in the war with the Han Dynasty, the Xiongnu ** for the north and south Xiongnu, the Southern Xiongnu in order to survive attached to the Han Dynasty, the Northern Xiongnu were finally forced to move west to the more fertile Central Asian steppes to seek survival, and the great migration of nomads also began. The northern steppe of the Ming Dynasty has not formed a huge and lasting nomadic empire, the reason is that the strong military defense system of the Ming Dynasty made the Great Khan of Mongolia mostly failed in the war with the Ming Dynasty, so it was unable to continue to unite many small tribes, but for the Ming Dynasty, the cost of the war was much higher than the cost of the first cost, and the final continuous war caused the financial poverty of the Ming Dynasty, and the financial income came from the people, too many wars made the court draw too much from the people, and the folk wealth of the Ming Dynasty was not as good as that of the Song Dynasty. 
The rise of Mongolia lies in the fact that Genghis Khan's victories in the battles of the Western Liao and Jin Dynasty again and again, each war has yielded a lot of harvests, and the Khan's power has been consolidated. The tribal alliance adopted by the steppe empire, the Khan's decision needed the support of the chiefs of the tribes, and therefore the military aristocratic democracy was often adopted in the nomadic empire. Whether it is the Kurultai Conference in which the Mongol tribes elected the Great Khan, or the Eight Kings Council before the Qing Dynasty entered the customs, it is a manifestation of this military aristocratic democracy. 
For the steppe, the Great Khan had to be able to fight well to maintain the unity of the tribal alliance, so the succession system on the steppe was different from that of the Central Plains Dynasty. For the Central Plains, imperial governance was accomplished by a vast bureaucracy. The monarch is mainly to bypass the bureaucratic system to govern the country will definitely have problems, the monarch's ability can only be ranked second, the first is the legitimacy of the monarch, the inheritance of the eldest son helps the stability of the country, the logic of the continuation of the Central Plains Dynasty lies in stability, which can be seen from the middle and late Qing Dynasty, the Qing Dynasty's nine sons to seize the heir to the country caused internal friction, cannibalism, and national turmoil, and Yongzheng took a secret reserve, which helped stabilize the court, Qianlong, Jiaqing, Daoguang all chose the most stable primogeniture inheritance system, However, with the death of his son-in-law, he was forced to adopt the strategy of establishing a virtuous person. As a traditional Central Plains dynasty, the Ming Dynasty has always implemented this point, and there is no grandson, so that the imperial power can be smoothly transitioned. Unlike the Grass Principle, the youngest son could not be guaranteed to be able to fight well, and the tribal alliance would inevitably dissolve once the Great Khan died. Therefore, the inheritance rule of the steppe is from brother to brother, rather than from father to son, so as to ensure that the heir to the throne is always a young man with strong combat effectiveness. Xiongnu lineage
But once all the brothers of the Khan who founded the steppe empire died, who should be the khan? More than one of the sons and nephews will come out in the hope of inheriting the throne, because their father had served as the khan, so there will be disputes, tribal alliances, and civil wars. This constituted a periodic succession crisis of the steppe empire, which would lead to the collapse of the empire. Hulu has no luck for a hundred years, and the pure steppe empire rarely lasts for more than a hundred years. This is due to the natural lifespan of the brothers of the Great Khan, who together do not live for more than a hundred years, and when they all die, the next generation will definitely happen**. As long as the Grassland Empire happens, the Central Plains Empire, which was not its opponent in terms of force, will have the opportunity to divide and rule. The conquest of the Xiongnu and the Turks by the Han and Tang dynasties was not fundamentally conquered by force, but was achieved by finally waiting for the latter to have an inheritance crisis that led to the occurrence of internal **, and taking advantage of the opportunity to divide and exploit. The rebellion of the younger brothers of the Khitan Yelu Abaoji, the same is true, the two hundred years of civil strife in the existence of the Liao, as long as the Khitan surname Yelu is surnamed Yelu, they all think that they have the opportunity to become the emperor of the Khitan, the Liao Dynasty is a dualistic system of the country, the emperor is the Khan of the grassland tribal alliance, and the emperor of the Han land of the sixteen states of Yanyun, and the wealth of the Han land of the sixteen states of Yanyun is conducive to supporting the emperor's military strength, which can quell the rebellion, and the imperial power is handed over to the emperor himself. In the later period of the Liao State, the imperial examinations, which initially existed only in the sixteen states of Yanyun, gradually spread to the grasslands, strengthening the authority of the monarch. 
As early as the tribal period, the Jin Dynasty adopted the elder brother and the father and the son, and the eldest of the heirs inherited the position of the tribal chief, so that the Wanyan Department became stronger and stronger, and finally could swallow Liao and destroy the Song Dynasty, but with the entry into the Central Plains, the inheritance system changed, the election system of the tribal alliance hindered the emperor's centralization of power in the Central Plains, and the Hailing King Wanyan Liang moved the capital to Beijing, and the new order was re-established. The power of the nobles such as Meng'an Mouk was weakened and eventually rebelled, and his successor, in order to quell the rebellion, reaffirmed Meng'an Mouk, and eventually the nobles held more power, and the ministers interfered in politics, hastening the demise of the Jin Dynasty. The Khan of the Mongol Empire is the need for the leaders of the tribes to elect the heirs, to the Kublai Khan period, Kublai Khan got the support of the Han land, after the death of Meng Ge held the Kuritai Assembly called Khan, although his younger brother Ali Buge also in the steppe was supported by the steppe departments, but the power of the steppe can not be compared with the unified Central Plains power, and finally Kublai Khan defeated Ali Buge and became the Great Khan of the steppe, the emperor of the Central Plains, Kublai Khan adopted the primogeniture inheritance system, The emperors of the Yuan Dynasty after that were all from the Zhenjin lineage of Kublai Khan's sister-in-law.