Urbanization has a tremendous number of impacts, both positive and negative.
The positive impacts of urbanization are typically economic and cultural. When cities arise, countries typically become more prosperous. The amount of labor and talent that is pooled together in cities makes them attractive places for businesses to start up. In the country, there are simply not enough concentrated human resources to allow large businesses to start up. These businesses help to drive economic growth. Cities are also attractive in cultural terms. They allow people to enjoy things such as the arts that might not be available in smaller places. They also allow cultural mixing and make for a more diverse and tolerant society.
There are many negative impacts as well. Perhaps the most obvious is the overcrowded and squalid conditions in which many newcomers to cities live, particularly in the early stages of urbanization. This can lead to things like crime and is also a major reduction in quality of life. Urbanization can also lead to environmental degradation as cities become sources of concentrated pollutants. Finally, cities can be socially problematic as traditional forms of social control break down and lawlessness and social problems such as homelessness arise.