We have long celebrated the ascent of the middle class — from China to the Arab world — as a critical piece in the emergence of open societies and a liberal world order. Scholars and pundits have reassured us that economic liberalization will give rise to powerful middle classes, which will eventually bring about democratic forms of politics. Baked into this argument is the assumption that assertive middle classes are crucial for the triumph of political liberty.

But in the last decade, these hopes have been shattered. The global spread of middle-class society and culture has not resulted in political liberalization. Quite the opposite: The growing middle classes across Africa, Asia and the Middle East seem disinclined to push for democratic reform, while segments of the European and American middle classes, feeling threatened by the rapid socioeconomic transformations of our time, have proven quite open to the appeals of illiberal demagogy. So why did political scientists place so much faith in this social group?

For one thing, the historical record seemed clear — middle classes have often stood at the forefront of the struggle for political freedom. Over the course of the modern period, as the rural and urban middle classes emerged as an increasingly powerful social group between the aristocracy and the peasants and workers, they began to challenge the powers and privileges of the old, entrenched authoritarian elites, fighting for the protection of private property, freedom of speech, constitutional rights and democratic participation, and the rule of law. Consider the central role of the middle classes in the great bourgeois revolutions of the late 18th and early 19th centuries (mainly in the Atlantic world), of the mid-19th century (mainly in Europe), and the early 20th century (mainly in Asia), all of which sought to limit the powers of monarchs.