How does it come about that individuals who genuinely desire to live in an ethnically mixed neighborhood nevertheless collectively, against their best intentions, produce a segregated town as they each seek optimal housing for themselves?

This model, proposed by the economist Thomas Schelling in 1971, at the time addressed a very important, and current, political issue: how to explain racial segregation in American cities. Specifically, Schelling wondered whether segregation was necessarily the result of racism—the prejudice of individuals of one race against those of another. Indeed, a frequently adopted mental model is that the overall state of segregation merely translates, by aggregation, the racism of individuals. If people actively wanted to live with others of a different color, or did not care at all about their race, then we should find that, globally, neighborhoods mix the different colors. Is this implicit model correct? In other words, does a global segregated state necessarily imply an individual preference for segregation?