Being the Old World, Europe achieved higher population density much sooner than the USA. High population density is strongly correlated with both socialism and losing religion. Big government is required to make high density living possible. In an all out world war, a few nukes would change the popularity of living in a nuclear target zone overnight. During the last world wars very few farmers were bombed or fire bombed into oblivion. It was mostly the godless snotty urban city slickers that got it.
Good point.