For a long time in Chinese history, the center of the entire Chinese civilization was mostly in the north. Specifically, it is in the Shaanxi area of Henan, where the so-called Central Plains are located.
To a large extent, this is determined by the geographical environment, the northern region is vast, the terrain is flat, especially in the Central Plains, the land is fertile, the climate is suitable, the environment is comfortable, and it is suitable for the development of agricultural civilization. Therefore, this place has always been a place where the masses must compete, and the so-called deer chasing the Central Plains is like this. The South, on the other hand, clearly does not have such conditions.
The development of the south is much later than that of the north, and its humid and hot climate inhibits the development of agriculture, and the geographical conditions of dense forests and hills hinder the exchange between regions, which is not conducive to the expansion of population and the development of civilization.
For example, the State of Chu in the Spring and Autumn Period and the Warring States Period had the largest territory among all the princely states at that time, but it was only one of the Spring and Autumn Great Powers and the Seven Heroes of the Warring States, and could not be claimed to be the strongest. Because its so-called territory is large, it does not represent the land population. At that time, the settlement area of the Chu State was mainly concentrated in the Yangtze River Basin. To the south, in fact, the influence of the Chu state is quite small. For the Chu state, it was a barbaric land, far less attractive than the bustling Zhongyuan.
Therefore, the kings of Chu in the past were fierce and wanted to conquer the Central Plains.
Of course, in the Warring States period, the State of Chu once forced itself to the Jianghuai region by expanding to the land of Wuyue, and its national strength was strong. But why was it still often beaten by the Three Jins and the Qin State?
In fact, only in terms of superficial strength, the expanded Chu state can be said to be the strongest in the Warring States. But the biggest problem with the Chu state is that the power is too dispersed. The State of Chu was different from those princely states in the north, in that it was a collection of nobles, that is, the country was controlled by some large clans, and the influence of the King of Chu was relatively small, and it could not effectively concentrate its strength every time it was conquered.
The important reason for this situation is because of the geographical environment in the south, under the division of mountainous forests, the closedness between various parts of the Chu state is relatively strong, and it is easy to form a strong regional force. Therefore, at that time, the Chu State could not stop moving the capital, because there was no place too central, and it was also possible to change the capital.
This also illustrates the relatively backward development situation in the south from the side.
Another example, such as Eastern Wu during the Three Kingdoms period, only in terms of area, did not lose to Cao Wei. But in fact, it has only three states. Moreover, the population was only half of that of the State of Wei.
I know that during the Northern Song Dynasty, the Lingnan region was still a remote and barbaric land. Therefore, Su Shi was exiled to this place because of the Wutai poetry case, because the exile was for you to suffer, not to enjoy happiness. Of course, Su Shi is a very open-minded person, and he can find fun in Lingnan, which has the famous sentence of "three hundred litchi in the day and do not quit being a Lingnanian".
Of course, it does not mean that there was no expansion to the south, and successive dynasties in Chinese history have developed the south and expanded for a time. For example, during the Qin Dynasty, Qin Shi Huang sent Zhao Tuo to lead 500,000 troops to march south to Baiyue, and included the Lingnan region into our Chinese territory, which also included the northern region of present-day Vietnam. Later, the Han Dynasty set up four counties in Lingnan, three kingdoms and so on.
So to be precise, the South is the result of expansion.
The so-called no expansion to the south is actually the southern part of our current territory, that is, southeast Asia. In fact, this is the same as the previously mentioned truth, it is too difficult to develop to the south. It took more than a thousand years for the kings of China's dynasties, until the Southern Song Dynasty, that the south gradually caught up with the north.
That's already doing its best, and then going further south, in fact, there is a feeling of being out of reach.
You know, even in the gun-and-gun modern era, no one can get a benefit in the dense forests of Southeast Asia. When the United States was so strong, was it not gray and slippery? In ancient times, the transportation was inconvenient, the environment was harsh, and the so-called advantages of national strength were offset to the greatest extent. How about a lot of weapons, you first go out of the primordial deep forest and then fight with us?
In general, the northern part of the Indochina Peninsula is mountainous, and the flat land is mostly fragmented and lacks large flat land. At the same time, there are many tropical jungles in the northern mountains, which I need not say more, and modern armies are often a little weak to deal with tropical jungles, not to mention the ancient times when the level of technology is not high.
From a military point of view, this terrain is not conducive to large-scale marching, but is conducive to small troops engaged in sparrow warfare.
In fact, many dynasties in Chinese history have tried to expand. For example, the Yuan Dynasty and the Ming Dynasty have all fought in Vietnam, but in the end they have not been able to effectively control this place, which is really too far.
Moreover, like the previous Chu state, they actually did not have much interest in these places, and if they could conquer it, of course, it was best, and if they could not, they did not need to force it. As long as you don't make trouble. If you are obedient as a vassal state, you can also send you red envelopes.
In other words, the Pearl River Basin was the limit of the expansion of the Central Plains Dynasty to the south, and in this state, expanding to the Indochina Peninsula would cost huge manpower and resources, and often the benefits would not be great. Therefore, due to the principle of cost and benefit, it is generally difficult for any dynasty to be interested in the Indochina Peninsula. Coupled with the fact that controlling the Indochina Peninsula was a loss-making transaction that could not recover the cost, the policy of the Central Plains Dynasty towards the Indochina Peninsula was often to establish clan relations.
As for the matter with the nomads in the north, it was really a helpless move. Like the wild lands in the south, the grasslands of the nomadic peoples in the north, in fact, most of the Central Plains dynasties are not very valued, just bitter cold lands. The reason why you and the nomads have been fighting for many years is that people are going to fight you.
They are hungry for the wealthy population of the Central Plains, and they just want to rob them, which is a source of contradictions between the two sides.
Moreover, relatively speaking, the nomadic peoples in the north are more threatening, and after absorbing the agricultural civilization of the Han people, they are often able to rise rapidly, either to compete with the Central Plains Dynasty or to annex the Central Plains Dynasty.
In other words, the northern peoples were a time bomb for the Central Plains Dynasty. Therefore, the Central Plains Dynasty, regardless of whether the emperor was Han or not, was often very sensitive to the northern problems, and even if it lost money, it was necessary to solve the problems in the north. One of the best solutions to this problem was the Qing Dynasty, which cut off the last hope of The Mongol revival and made the Mongols the northern barrier of the empire.
To sum up, the threat of the northern nomads to the Central Plains Dynasty is too great, and it must be solved, and if it is not solved, the country will be destroyed. Due to the geographical environment, the south is not closely related to the Central Plains Dynasty. And the south is located in the wilderness, the Central Plains Dynasty is not interested in it, and the local indigenous strength is too weak, not a threat to the Central Plains Dynasty, naturally there is no need for too many disputes.