This dissertation proposes a new, synthesized perspective for explaining the "Nonmetropolitan Turnaround" in the 1970s and 1990s. By studying the definition of urbanization carefully, using the human ecological perspective, many processes happening during the "Nonmetropolitan Turnaround" in the 1970s and 1990s, such as suburbanization, deconcentration, and counterurbanization, can be understood as different forms of the urbanization processes. When the majority of the population was rural, the dominant pattern of urbanization was rural-urban migration. When the majority of the population became urban, the dominant urbanization pattern reversed to urban-rural migration because urban centers had reached beyond their optimal density and processes operated to reduce their density. This paper hypothesizes that the two "turnarounds" were simply the result of different aspects of urbanization complicated by metropolitan status reclassifications. The perspectives of suburbanization, counterurbanization and deconcentration are integrated into the urbanization perspective. Using migration flow data compiled by the Census Bureau from 1975 to 1980 and from 1995 to 2000, the summary analyses confirmed that the net migration due to the three forms of urbanization largely accounted for all of the net migrant flows. This dissertation further tested the validity of optimal density theory with net migration data and confirmed the utility of this perspective in predicting the direction of net migration.