Why didn't China want Vietnam before, but the mountainous areas of Yunnan?

1. Northern Vietnam is mountainous, and the climate is not conducive to the production and life of Han people without modern medicine.

2. In China, Yunnan was really digested in the Ming and Qing Dynasties (Taiwan Province Province was actually occupied by the Qing Dynasty), and it took longer to go south. Obviously, because of the western colonists, there is no such time.

Because Viet Nam is in the tropical rain forest, China immigrants can't live a good life. Vietnamese can live on wild fruits, and this climate and terrain are not conducive to the combat effectiveness of farming people.

Vietnam has a long and narrow terrain, and the west is full of mountains. After the Vietnamese attacked us, they could quickly escape into the western mountainous areas and tropical rainforests, which also limited the mobility of our army. Therefore, in the Ming Dynasty, the fact that our Vietnamese tax revenue was tens of thousands of dollars and the military expenditure was several million dollars was formed. If you can't make ends meet, you can't take it.