Racial, ethnic, and religious tensions are common around the world. Some states collapse under their weight; in less extreme cases, states’ functions are negatively affected. Economists have recognised the importance of this factor in explaining poor economic policymaking, low quality of government, and delays in development.

One of the (many) reasons why the Nobel laureate Thomas Schelling became famous was his analysis of sorting and segregation. He showed that differences in tastes about the kinds of people with whom one wanted to interact would lead to intensely segregated social environments.