The end of the Cold War three decades ago followed by the terror attacks in 2001 should have ushered in an era of consensus and low-intensity politics in the United States. That was the expectation at the time—but it turned out to be wrong. Over the past few decades Americans have turned on themselves, dividing into hostile tribes and parties with little common ground to hold the national enterprise together. As a result, as many now agree, the United States finds itself more polarized and divided over politics than at any time since the 1850s. But today, in contrast to the slavery issue of the 1850s or the Great Depression of the 1930s, there is no single crisis or line of conflict to account for the situation. We live in a time of general peace and relative prosperity and do not face any single challenge comparable to slavery or mass unemployment. America is coming apart, but no one can quite explain why.

Today’s polarized politics is different from the push and pull by different economic and cultural groups that has always been an aspect of the American scene. The variety of groups contending for influence has generally been seen as a strength rather than as a weakness of the American system. James Madison said it best in Federalist10: the sheer multitude of factions in a large republic like the United States preserves it by preventing any single faction from gaining the upper hand. The problem today is that