Today's cities can be targets of criticism, but they're nothing compared to what people faced in late 19th-Century America, according to Laura Bliss of CityLab.
Families lived cheek-to-jowl in tenement districts near polluting factories, and they walked on streets filled with fetid, uncollected human and animal waste. Noxious fumes frequently seeped over to higher-end homes and businesses, too. Without proper sewers or drinking water systems, infectious disease proliferated.
To solve these problems cities turned to zoning and, over time, economists found that zoning changed land uses.
Lot by lot, they found significant variation between the activities that predated zoning and those that came after, especially as years went by. For example, some factories and shopping areas that didn’t conform to the 1923 code were allowed to stay in their respective locations, thanks to a “grandfather” clause. But over time, the vast majority of them disappeared.