Is it because the main force of Yuan soldiers was able to flee to Mongolia in the north, and the Ming Dynasty could not conquer Mongolia?

If the Yuan Dynasty still had the main force, it would not have fled to its hometown in Mongolia. Since it is to flee back, it is because the Mongols also feel that the tide is gone and there is nothing they can do. As for why Mongolia has never been conquered, it is because Mongolians are very tough nomadic people, who fight and run and live on weeds. Of course, under the condition of poor mobility of the troops at that time, they could not be conquered This is the same reason that Qin Shihuang built the Great Wall at that time, because to some extent, the Han people had no choice but to guard against the floating ethnic minorities, and sometimes they were even humiliated, such as the pro-democracy policy.

Moreover, the army can be alive. As long as the nation does not fall, even if the main force was defeated in the past, just take a break and make a comeback, hehe.