The Mongolian empire obviously has a large territory. Why didn't the Ming Dynasty inherit it completely?

The Ming Dynasty was established on the basis of the Yuan Dynasty. However, the establishment of the Ming Dynasty only regained the place where the original Han people lived. There is no real dabbling and conquest of the Mongolian grassland, the hometown where the Mongols live, and the Four Great Khan countries established by the Mongolian Empire in the process of the Western Expedition. When Xu Da occupied the Yuan Dynasty and drove the whole Mongolian forces back to the grassland, in fact, the Mongols at this time still controlled many areas north of the Great Wall. However, the area south of the richest Great Wall, which was originally under its jurisdiction, was lost.

The Mongols who retreated to the grasslands still have strong military and economic strength. In order to completely eliminate the threat of Mongols to the south of the Great Wall, Zhu Yuanzhang and the later rulers of the Ming Dynasty actively organized many northern expeditions. Although it hit the spirit of various tribes in Mongolia, it never wiped out the Mongols. Besides, the Mongols are still very powerful internationally. The whole of Central Asia, West Asia and South Asia is still dominated by Islamized Mongols.

When Zhu Di, the emperor of Ming Dynasty, was in power, he also actively fought against Mongolia. However, due to the production and lifestyle of the people in the Central Plains, it was far from the nomadic culture of Mongolian grasslands. Although some Mongolian-dominated health centers were established, there was no way to win over the Mongols who lived by water and grass. The natural allies of the Ming Dynasty gradually joined Gao Liguo in the Eastern Peninsula and Vietnam in the south, but these were just East Asian cultural circles.

It was the Manchu forces who finally won Mongolia. They gradually controlled the whole Mongolian grassland through marriage. Later, it actively implemented the way of disintegration and attack, and finally turned this Mongolia with a population of nearly 1 million into a small tribe with a population of only a few hundred thousand.