On urbanization and population migration

The processes of urbanization are depended to a certain degree on the development of human societies.There were noon-markets at fixed locations without city walls at first,and people just gathered,traded goods at noon and then left the markets for home.In the slave society and feudal society,towns with city walls appeared.But the scales of towns were still small,and people still traded goods and then left for home.In capitalism society,agricultural population flooded into cities and settled down.The rapid expanding of cities brought many adverse side effects.City walls lost their safeguard function,became a barrier to the expanding,and were torn down.Then the development of cities entered the stage of counterurbanization.With the human societies developing to a higher stage,the difference between urban area and countryside will narrow down and disappear.People can migrate freely.