Vietnam was accepted as the territory of Daming after the war. Why is it gone in less than 30 years?

With the collapse of the Tang Dynasty, the Liu regime of the Southern Han Dynasty in the Five Dynasties and Ten Countries partially controlled Vietnam, but with the shrinking power of the Song Dynasty, Vietnam was once again separated from the territory of China. After the establishment of the Ming Dynasty, he tried to recover Vietnam. At the end of the Ming Dynasty, he sent Zhang Fu, a British public servant, to send 500,000 troops to Vietnam, reintegrated them into Chinese territory, and set up a chief secretary. However, in less than 30 years, the Ming Dynasty voluntarily gave up Vietnam's status as a directly administered territory, recognized its relative independence and made it a vassal state. The main reasons are as follows:

First of all, Vietnam has a humid climate and is not suitable for living. In order to stabilize Vietnam, the Ming dynasty stationed troops in Vietnam, which often did not adapt to the climate in Vietnam, resulting in frequent epidemics.

Second, Vietnam became a heavy financial burden in the Ming Dynasty. Although Vietnam can be taxed locally if it is included in the territory, the income tax is very small, with a maximum of less than 72,000 yuan. In order to maintain the rule, the court had to send officials at all levels and troops to maintain public order and border defense, which required a lot of money. For the court, it is serious to make ends meet. Many ministers think that it is not worth the loss to incorporate Vietnam into the territory and advocate giving up Vietnam.

Third, Vietnamese aborigines have tough folk customs, forming a relatively independent nation and ruling force. Although suppressed by force, local forces continued to resist the rule of the Ming Dynasty. In the long run, the empire thought Vietnam was a chicken rib and finally chose to quit Vietnam.