“We cannot all live in cities, yet nearly all seem determined to do so,” New York editor Horace Greeley complained. The last three decades of the nineteenth century witnessed an urban explosion. Cities and towns grew more than twice as rapidly as the total population. By 1900, the United States boasted three cities with more than a million inhabitants—New York, Chicago, and Philadelphia.

Patterns of global migration contributed to the rise of the city. In the port cities of the East Coast, more than fourteen million people arrived, many from southern and eastern Europe, and huddled together in dense urban ghettos. The word slum entered the American vocabulary along with a growing concern over the rising tide of newcomers. In the city, the widening gap between rich and poor became not just financial but physical. Changes in the city landscape brought about by advances in transportation and technology accentuated the great divide in wealth at the same time they put physical distance between rich and poor.