How did the creation of suburbs extend and reinforce economic and social segregation in the United States?
Suburbs make their first real appearance in the United States in about the 1950s, and especially in the 1960s as America's interstate highway system was completed, increasing peoples ability to move themselves and goods and services more cheaply and easily.
This came shortly after the urban African-American population exploded during and after World War II. I don't think one can argue that suburbs were created with segregation in mind, but I don't think they are unrelated either. Americans of that time period were much more likely to have racial prejudices than today, and with that increase in the number of urban black neighborhoods, there was "white flight" from the cities to the suburbs. The fact that living in the suburbs and commuting became much more affordable simply accelerated that process.
This brought down real estate prices in the major cities, attracting immigrants and the American poor--which included African-Americans in large part at that time--to the cities. So I believe that the segregation we see in the suburbs can be directly tied to racism, but more so because of economic disparities between those races.