Liberal policy makers have long regarded Scandinavian policies as a model. If a welfare state can work there, they have long argued, it can work here. But the Scandinavian countries have homogeneous populations with high levels of trust, conscientiousness and social connectedness. It is not a coincidence that in the two states with the highest levels of the social connectedness Mr. Putnam described, North Dakota and Minnesota, most people are of Scandinavian or German descent. But policies that work well in Scandinavia or Minnesota and North Dakota won’t necessarily work well in a wider United States, where a much larger proportion of people are socially disconnected.

And such policies may not work as well as they might have in the United States of the 1950s and early 1960s, in which disconnectedness was much less common. That was an America in what I call the Midcentury Moment, a period when World War II and unexpected postwar prosperity produced a conformist and (mostly) culturally homogeneous nation with low rates of divorce and single parenthood, and high rates of social connectedness. A nation accustomed to a universal military draft and wage-and-price controls, and in which increasing numbers worked for giant firms and were members of giant labor unions, probably would have been more amenable to a centralized command-and-control policy like ObamaCare than the culturally fragmented America of today.

In the long run of American history, the Midcentury Moment was just that—a moment, an exception, not the rule. We have been in some sense a multicultural nation from our colonial beginnings. The Founding Fathers, seeking to unite Puritan New England, Anglican Virginia, Dutch New York and Quaker Pennsylvania with the Scots-Irish warriors on the Appalachian frontier, determined that the federal government would impose no religious test for office and make no law regarding a religious establishment. They provided for a limited central government and a wide free-trade zone in which local cultures could prevail, local preachers could convert, and local entrepreneurs could innovate.