It’s hard to overstate the value of WWII in reshaping American demographics. Millions of men were relocated. This constituted a kind of information-shock, as they found that, huh, they really liked living in California, or Florida, or Texas, or Arizona, instead of Illinois or Pennsylvania. In the prewar economy, large amounts of welfare-improving migrations did not occur (indeed the depression and 20s had strikingly low migration) thanks to resource constraints on migrants, but also information and social constraints.