Although in ancient Chinese history, great unification was the mainstream and the trend of the development of the times. However, "the general trend of the world will be divided for a long time, and it will be united for a long time", so there have been many periods of great division and great chaos.
Curiously, most of the dynastic wars fought to end the Great Schism and Chaos were won by regimes or military groups occupying the north, for example, the Western Jin Dynasty that ended the Wei and Jin Dynasties was the Western Jin Dynasty, and the Northern Song Dynasty that ended the Five Dynasties and Ten Kingdoms (in fact, the Northern Song Dynasty was also partially unified). The only exception is Zhu Yuanzhang, whose capital is Nanjing, and has achieved unification from south to north. In fact, in the history of China, there are many people who have almost achieved the feat of unifying the whole country from south to north, such as Huan Wen and Liu Yu of the Eastern Jin Dynasty, but they have not been able to complete this feat. The reasons for this are probably as follows.
First of all, the economic strength of the north occupies an absolute advantage. In ancient China, which was based on agriculture, agriculture was the economic lifeblood and main source of taxation for a regime. Therefore, the more developed the agriculture of a country or regime, the stronger its economic strength. Although, the southern land is vast and very suitable for farming. However, in the south, where the land is vast and sparsely populated, farming technology has long remained in the stage of "slash-and-burn farming". On the contrary, the farming technology of the north is far ahead of the south, not only using a lot of iron and curved ploughs, but also building many water conservancy projects. Developed agriculture can not only guarantee the country's taxes, but also allow the country to have a large population. Taking the Three Kingdoms as an example, Sun Wu (2,562,000 people) and Shu Han (population 1,082,000 people) in the south, the total population of the two countries combined, is not as large as Cao Wei (4432881 people). It is precisely because the north has developed agriculture that it can provide sufficient material and manpower support during the successive dynastic unification wars.
Although China's economic center of gravity has shifted south after the Song Dynasty, the second advantage of the north has begun to appear. That is the military that occupies overwhelming force. In the era of cold weapons, military superiority is mainly reflected in the number of troops and the quality of the army. Because the North has a long-standing economic advantage, it can quickly assemble and arm a large army. For example, when the Sui Dynasty launched a unified war, it was able to dispatch a five-way army with a strength of about 500,000 troops, so that Southern Chen was invincible and could only accept the fate of destruction.
At the same time, due to the abundance of pastures in the north, large cavalry corps could be formed. Although war horses were also raised in the South, the number and quality of war horses were far inferior to those in the North. Taking the Yue family army of the Southern Song Dynasty as an example, through procurement from the north and the warhorses captured in the war, a cavalry of about 8,000-10,000 people was formed. However, the number was far inferior to that of their rivals, the Jin army, which alone dispatched 15,000 elite cavalry, including the "Tiefu Tu" and the "Kidnapped Horse". The South was already inferior in the number of cavalry, and the gap in the quality of cavalry was even greater. Taking the Song Army as an example, the Song Army stipulated that the height of warhorses was between "four feet and one inch" and "four feet and seven inches" (about 127 centimeters to 146 centimeters), but in fact it could not be reached at all, so the actual height of many warhorses of the Song Army was below four feet and one inch. In contrast, the northern war horses are basically around 140 centimeters.
The height of the war horse will directly determine the weight that the war horse can carry. Taking the Southern Song Dynasty war horse as an example, although the "big full" horse armor and the "small full armor" horse armor have been invented, the weight of a cavalry armor has been 20 kg to 25 kg, plus weapons and equipment, it has reached about 50 kg. Therefore, the vests of the Song Army's war horses were mainly leather armor, such as "money zhu patent leather harness suit" and "steel zhu patent leather harness suit". However, among the opponents of the Song Army, the Western Xia had "iron harriers" and the Jin Dynasty had "iron floating tu", both of which were cloaked in iron armor made by cold forging. While enhancing the protection ability, it also improved the impact ability of the heavy cavalry.
Due to its superiority in both the number and quality of the army, the North had an absolute advantage in the wars of dynastic unification. However, if there is great turmoil in the northern region and military geniuses in the south, it will indeed make up for the economic and military gap between the two sides, and even win the final victory, such as Zhu Yuanzhang's establishment of the Ming Dynasty is a very good example. But often in times of chaos in the North, the military geniuses of the South also face internal and internal problems.
Liu Yu, the Later Emperor wu of the Song Dynasty, for example, recovered almost the entire area south of the Yellow River and Guanzhong, known as the 800-mile Wilderness, during the Northern Expedition from the twelfth year of Yixi (416 AD) to the thirteenth year of Yixi (417 AD). Before Liu Yu, Huan Wen, a powerful minister of the Eastern Jin Dynasty, also carried out the Northern Expedition three times, all of which achieved great results, and even once recovered Luoyang, the former capital of the Western Jin Dynasty. What is even more legendary is that Chen Qingzhi of Southern Liang, who only commanded 7,000 "white-robed troops", once swept through the Northern Wei. However, after creating many military miracles, they failed to achieve dynastic unification. The reason for this is "backyard fire".
Just as Liu Yu was preparing to travel north, in the hope of consolidating the newly recovered land and continuing to expand his battle record. Liu Muzhi, a confidant who was sitting in the capital, died suddenly, and he was bent on taking Sima Shi's place, fearing that his roots in Jiangnan would be shaken, so he could only hurried back to his division. The purpose of Huanwen Northern Expedition was to establish his authority in the Eastern Jin Dynasty in order to further become emperor in the future. Therefore, he did not dare to stay away from the Eastern Jin Court for a long time, and every time the Northern Expedition was a shallow taste, he quickly returned to the Dynasty after achieving certain achievements. Although Chen Qingzhi did not have the ambition to trespass, he only had 7,000 lone troops, and in the absence of aid and food supplies, he could only return home in the end.
It can be seen from this that in the dynastic unification war in ancient China, the reason why only Zhu Yuanzhang won the final victory from the south to the north, in addition to economic and military reasons, the most critical thing is the human factor.