The paper by Cutler, Glaeser, and Vigdor (1999) examines the rise and decline of racial segregation in American cities from 1890 to 1990. It finds that segregation increased dramatically from 1890 to 1940 as blacks migrated from the rural South to urban areas, leading to the formation of ghettos. From 1940 to 1970, segregation expanded as blacks continued to move into urban areas, resulting in the dominance of ghettos in central cities. However, after 1970, segregation declined as blacks moved into previously all-white areas, particularly in the South and West. The study shows a strong positive relationship between urban population density and segregation. Data on housing prices and attitudes toward integration suggest that segregation in the mid-20th century was a result of collective actions by whites to exclude blacks from their neighborhoods. By 1990, the legal barriers enforcing segregation had been replaced by decentralized racism, where whites pay more than blacks to live in predominantly white areas. The paper also discusses three theories of segregation: the "port of entry" theory, where blacks prefer to live among their own race; the "collective action racism" theory, where whites use legal or illegal barriers to exclude blacks; and the "decentralized racism" theory, where whites segregate themselves by paying more to live with their own race. The study uses data on housing costs and segregation indices to test these theories and finds that segregation was enforced by collective actions by whites in the mid-20th century, but by decentralized racism by 1990. The paper concludes that segregation is most persistently related to city size, with larger cities being more segregated. The study also finds that the decline in segregation after 1970 is due to the integration of previously all-white areas and the movement of blacks into these areas. The paper highlights the importance of understanding how neighborhoods are formed and the role of economic and social factors in shaping segregation patterns.The paper by Cutler, Glaeser, and Vigdor (1999) examines the rise and decline of racial segregation in American cities from 1890 to 1990. It finds that segregation increased dramatically from 1890 to 1940 as blacks migrated from the rural South to urban areas, leading to the formation of ghettos. From 1940 to 1970, segregation expanded as blacks continued to move into urban areas, resulting in the dominance of ghettos in central cities. However, after 1970, segregation declined as blacks moved into previously all-white areas, particularly in the South and West. The study shows a strong positive relationship between urban population density and segregation. Data on housing prices and attitudes toward integration suggest that segregation in the mid-20th century was a result of collective actions by whites to exclude blacks from their neighborhoods. By 1990, the legal barriers enforcing segregation had been replaced by decentralized racism, where whites pay more than blacks to live in predominantly white areas. The paper also discusses three theories of segregation: the "port of entry" theory, where blacks prefer to live among their own race; the "collective action racism" theory, where whites use legal or illegal barriers to exclude blacks; and the "decentralized racism" theory, where whites segregate themselves by paying more to live with their own race. The study uses data on housing costs and segregation indices to test these theories and finds that segregation was enforced by collective actions by whites in the mid-20th century, but by decentralized racism by 1990. The paper concludes that segregation is most persistently related to city size, with larger cities being more segregated. The study also finds that the decline in segregation after 1970 is due to the integration of previously all-white areas and the movement of blacks into these areas. The paper highlights the importance of understanding how neighborhoods are formed and the role of economic and social factors in shaping segregation patterns.