During the 1890s, the word segregation became the preferred term for the practice of coercing different groups of people, especially those designated by race, to live in separate and unequal urban residential neighborhoods. In the southern states of the United States, segregationists imported the word—originally used in the British colonies of Asia—to describe Jim Crow laws, and, in 1910, whites in Baltimore passed a “segregation ordinance” mandating separate black and white urban neighborhoods. Copy-cat legislation sprang up in cities across the South and the Midwest. But in 1917, a multiracial team of lawyers from the fledgling National Association for the Advancement of Colored People (NAACP) mounted a successful legal challenge to these ordinances in the U.S. Supreme Court—even as urban segregation laws were adopted in other places in the world, most notably in South Africa. The collapse of the movement for legislated racial segregation in the United States occurred just as African Americans began migrating in large numbers into cities in all regions of the United States, resulting in waves of anti-black mob violence. Segregationists were forced to rely on nonstatutory or formally nonracial techniques. In Chicago, an alliance of urban reformers and real estate professionals invented alternatives to explicitly racist segregation laws. The practices they promoted nationwide created one of the most successful forms of urban racial segregation in world history, rivaling and finally outliving South African apartheid. Understanding how this system came into being and how it persists today requires understanding both how the Chicago segregationists were connected to counterparts elsewhere in the world and how they adapted practices of city-splitting to suit the peculiarities of racial politics in the United States.