What does the term "urban sprawl" mean?
Expansion of urbanized areas
Due to industrial revolution, lots of rural people had to move to cities. Cities expanded remarkably. At the same time, people become richer and they wanted to have independent houses (instead of apartment flats).
Suburbs gained popularity although suburban areas were once agricultural fields or forested areas.
By urban sprawl it is underlined that urban expansion caused problems in once rural/natural areas. Urban sprawl has been observed in many cities in the US.