I’m not a free-market fundamentalist. To me, the beauty of liberal capitalism lies in its performance: More people live well, and live longer, than ever before. Millions of working-class people have moved from poverty to become homeowners and have seen their offspring rise into the middle class or higher.

Today this egalitarian capitalist progress is showing signs of fading, not only in the United States but also in Europe, Australia, and increasingly East Asia. This marks a drastic reversal from the conditions that prevailed after World War II, when the incomes of those in the lower quintile surged by roughly 40 …