D id Timothy Noah catch a wave or anticipate one? In 2010, Noah, a longtime public-policy reporter now at The New Republic , wrote a ten-part series in Slate about American economic inequality. This was at a time when the most discussed issue in U.S. politics was how much government Tea Partiers aimed to slash and how quickly we must balance the budget—even in the face of the worst downturn in eight decades. Then, about a year after the Slate series, Occupy Wall Street and its proxies around the country seemingly awakened the nation to the vast disparity of wealth between the top 1 percent and the rest of us. This was just in time for The Great Divergence , Noah’s expanded book on the subject, to refer to the movement in an introduction. On the other hand, important ideas may lie dormant for ages, unacknowledged beyond a few specialists—and then, suddenly, they pervade “the air around us,” as an old professor of mine used to say. So it is with the issue of inequality, whose current...