Why did the Northern and Southern Dynasties finally unify the whole country?

This inertia did exist in the early history of China, which was basically the unification of the southeast and northwest. Not to mention other periods, only the Northern and Southern Dynasties.

First of all, although the "Five Disorders" dealt a great blow to the population, economy and culture in the north, the northern Wei Dynasty unified the north, especially after Emperor Xiaowen moved south to Luoyang for full sinicization, the north did get a great recovery. Immigrants from the north brought advanced farming techniques to the south, but during the Southern and Northern Dynasties, the productivity level in the north was still higher than that in the south. In fact, culture and politics are the same. For the gentry in the Southern Dynasties at that time, those who were in power and made great achievements were northerners, while the local gentry in the Southern Dynasties were suppressed.

Secondly, the invasion and integration of the northern minorities really improved the overall quality of the North Korean army. Although the conclusion of Wolf Totem is nonsense, the "wolf nature" and "blood transfusion" in the Northern Dynasties are true, and the Han army in Sui and Tang Dynasties is also very strong. However, the Southern Dynasties relied on the Yangtze River natural barrier for a long time, and their military strength declined day by day. Zu Ti, Huan Wen and Emperor Wu of Song became legends, while Chen Qingzhi was just a flash in the pan. ...

Third, Emperor Xiaowen of the Northern Wei Dynasty sinicized and worshiped Buddhism, which influenced the thoughts of some Xianbei nobles. However, Gao Huan and Yu Wentai were not born noble. Later, the Guanlong nobles who relied on the Sui and Tang Dynasties were all generals from the Yuwen family in the Northern Qi Dynasty. Hu Feng is heavy and belligerent. Yuwen Yong's efforts to destroy the Buddha were greatly supplemented by human strength and financial resources. It was not until Yang Jianshi that his strength was overwhelming. However, in the Southern Dynasties, metaphysics and Buddhism were good for a long time. Xiao Yan was in a mess, and political corruption led to the chaos in Beijing, which was out of control!