U. S cities grew quickly during the early 1800's because

Cities grew quickly during the early 1800s because of industrialization and the growing need for factory workers as well as the decrease in the need for people to work on farms

Because there were many people from their native countries living there, There were several reasons why cities grew so quickly in the United States in the late 1800s. One reason had to do with immigration. Many immigrants were coming to the United States during this time.