 Throughout the 20th century, implementation of urban consolidation policies appears to come in 'waves', separated by population surges stemming from major events like World War I and II.Urban consolidation policies began to appear in the United States around the same time, with one of the earliest examples being a proposal for the consolidation of railroad lines in Iowa and Minnesota to increase the capacity and efficiency of existing passenger and freight traffic.Although urban consolidation policies may have many positive social, economic, and environmental effects, there are limits to the extent of its benefits.