When immigrants arrived to the East Coast of the United States in the 19th Century, they tended to move into neighborhoods in which members of their nationality already lived.
This was practical as the immigrants would be able to assimilate easier and would not feel as isolated in the new country. The established immigrants could also be a useful source of information and could help in difficult times.
These neighborhoods were located in the large East Coast cities and came to be small representations of the home country of the immigrants that founded them.
