The last decade has seen a number of progressive municipal leaders gain victory in major cities across the West. Over the weekend, two new mayors swelled their ranks: the Socialist Party’s Emmanuel Grégoire won a clear victory in Paris, while Green Party member Dominik Krause defeated the social democratic incumbent in Munich. These victories follow New York City’s democratic socialist Zohran Mamdani taking office in January.

These new mayors have seemingly bucked the trend of declining left-wing vote shares and the rise of the populist right at the national level. One reason for this trend is a backlog of political ambition: national democratic politics have become increasingly dysfunctional, with established parties often unable or unwilling to formulate programs of social transformation with wide appeal. And cities have become more socially homogenous in a way that favors such progressive reforms: the new urban electorate is increasingly well-educated and socially liberal.

But the reasons are not just cultural: cities benefit from what political scientist Theo Serlin calls a “public agglomeration effect”: urban economies of scale make government provision more efficient, which shifts city residents toward preferring more of it. And both middle-class voters and the urban proletariat are particularly exposed to the social dislocations that are more pronounced in urban centers and that require active public policy interventions: higher housing and rental prices, labor market competition, and cost-of-living pressures.