The 2008 financial crisis was devastating to the world economy. Just how devastating is something economists still argue over. It is not easy to add up the costs of bank bailouts, a lost decade of economic growth, spiking public debt, grinding austerity, and surging inequality. But the biggest cost of the crisis might be not economic but political: the populist wave that has swept over the world in the last decade, upending political systems, empowering extremists, and making governance more difficult. Financial crises regularly lead to political polarization and populism, but the recent populist surge has lasted longer than those that followed earlier crises—and done more damage.