With the sudden growth of cities, housing became scarce so some houses were divided into small apartments where entire families could cram into. What were these run-down neighborhoods called?

Tenement Housing

Explanation:

Tenement Housing or tenement started at the age of the Industrial revolution. As people moved more and more to cities, the housing became insufficient, so tenement housings emerged. These neighborhoods were mostly occupied the low-income workers, and are associated with slums and low classes.

Tenements are buildings with many occupants and small apartments that are rented. The whole family would live together in the apartment. These places were often uncomfortable, with little space and little lighting, and sometimes even unsafe, without any fire regulations and ventilation. They were especially developed and popular in Scotland and New York City.