Many new immigrants arrived in US cities in the first half of the 1800s. What was the main cause of the problems they encountered?

Cities grew rapidly as many immigrants arrived in the first half of the 1800s, but housing, sanitation, and other services did not keep pace. This left many newcomers facing crowded and difficult living conditions. The main cause was that cities were unprepared for so many new inhabitants.

AI-written and checked against the verified answer.