From a market standpoint, there are two main requirements that are met by the U.S. cities that undergo substantial effects of gentrification. These are: an excess supply of deteriorated housing in central areas, as well as a considerable growth in the availability of professional jobs located in central business districts. These conditions have been met in the U.S. largely as a result of suburbanization and other postindustrial phenomena. There have been three chronological waves of gentrification in the U.S. starting from the 1960s.