Answer:
urbanization
Step-by-step explanation:
Urbanization is a situation which caused by a population shift from rural areas into the center of the cities.
During the industrial revolution, Factories tend to be opened in the middle of the cities. This create a lot of job opportunities that attracted people from rural areas. So, a lot of them decided to leave their home town and live close to their workplace.
As the population in the center of the cities grow, other business started to be built in order to accommodate the people there. Small businesses such as diners, laundry place, bookstores, motels, etc started to appear and populated the area even more.