Putnam and Garrett take the data from diverse spheres and produce different versions of the same chart, which is an inverted U. Until the late 1960s, American life was improving across a range of measures. Since then, it’s a story of decay.

Why did all these different things happen in unison and then suddenly turn around all at once? Maybe economic change drove everything? But no, the timing is off. Economic inequality widened a bit later than most of the other trends. Maybe it was political dysfunction? Nope. That, too, happened a bit later.

The crucial change was in mind-set and culture. As Putnam and Garrett write: “The story of the American experiment in the twentieth century is one of a long upswing toward increasing solidarity, followed by a steep downturn into increasing individualism. From ‘I’ to ‘we’ and back again to ‘I’.”