The western area to the west of Hexi Corridor, Tibet and Yunnan in the southwest, the grassland to the north of the Great Wall and the northeast, based on the territory of Qin and Northern Song Dynasties, is the core area in the history of China. In this core area bounded by Qinling Mountains and Huaihe River, China is divided into two parts: the south and the north. There are great differences in natural geographical characteristics, vegetation ecological environment, cultural and historical traditions. Therefore, in the agricultural era, if the Northern Expedition was based in the south, it would be difficult to unify the whole country.
First of all, the south is mountainous and the north is plain. Therefore, as Yue Fei said, cavalry is good for peace and infantry is good for mountains. Soldiers in the south are more suitable for mountain terrain, and they are better at mountain fighting since childhood, while there are more cavalry and plains in the north, which are more suitable for large cavalry regiments. So the formation of a pattern is that the northern regime to enter southern operations, it is often not easy to adapt to the fighting in hilly areas. Besides, there are many rivers and lakes here, which is not suitable for playing in the water. So it is relatively difficult.
Actually, it's quite appropriate The regime with its capital in the south is either as weak in military capability as in the Song Dynasty, or as in the Ming Dynasty, that is, Zhu Yunwen. In fact, it didn't take long before Hong Xiuquan's regime came into being. Then, why are northerners stronger than southerners in history, and how often does the northern regime unify the southern regime? Some people say that in ancient China, the north was more developed than the south, so it had the power of unification. However, Jiangnan and Jiangbei are not separated by water.