This is the worst of times... but we've been here before. During the Gilded Age of the late 1800s, America was highly individualistic, starkly unequal, fiercely polarized, and deeply fragmented, just as it is today. As the twentieth century opened, America became more egalitarian, more cooperative, more generous; a society on the upswing, more focused on our responsibilities to one another and less focused on our narrower self-interest. Sometime during...