Trace the rise of medieval cities in Europe. Why did the cities develop a system of self-government?

With the development of production technology, the improvement of tools of labor, it became possible to separate handicraft from agriculture. To separate from the feudal-dependent population, artisans were forced to leave the villages for the cities, where it was possible to establish not only production, but also trade. So the number of urban residents began to increase. In the cities, there was a need to form self-governing bodies, because they were formally dependent on the government, but in fact they were independent.