A new book about Southlake, Texas discusses some of the mechanisms used to keep the community white:

These approaches are found across American suburbs. Start with zoning for larger residential lots which has several effects. It keeps houses further apart. It maintains a more rural image. It avoids having dense housing. It raises the price of homes as each lot is bigger and costs more and the houses can be bigger since there is more space to build.

Next, take apartments and why a good number of suburbanites do not like them. They are denser housing. Suburbanites prefer homeowners, who they think have more commitment to the community and to the property in which they live. They are cheaper and this may drive property values down.

Put these two together and suburbs can keep housing values up and limit who can live in a community. This is not an accident; suburbs often have particular residents in mind when they think about development and the future of their community.