Question

What problems were created by the rapid growth in cities ​

Answer 1

The main factor is probably air pollution. The more humans the more cars, busses, trains, etc. Transportation is a necessity especially in the 21st century. Also factories or incorporations can produce heavy amounts of toxic chemicals released into the air.

Answer 2

High population density leading to congestion, lacking infrastructure, lack of affordable housing, flooding, pollution, slum creation, crime, and poverty.