In my own words, how did the later rural fairs develop?

First of all, the key point of this problem is supply and demand.

With the development of market economy and the increase of population, people's demand for daily necessities and other materials is increasing. Besides, people have different skills and produce different products. People will trade in a suitable place to get what they want. Coupled with the needs of social management, it is necessary to divide a place in a region for trading, which is convenient for management.