But arguably the biggest future challenges facing the elite cities are those they impose on themselves. As cities, particularly in the West, increasingly become dominated by singles, their politics have shifted far to the left of the rest of their respective countries, notably on social issues and climate. In many cities, centrist and conservative politics have largely ceased to exist.

The trend towards one-party progressive rule has helped to undermine Barber’s claim that they are inherently more efficient, much less make them places ideally suited to “harbor hope.” Instead, they are now toxic to the aspirations of the middle class; according to Pew research, the greatest inequality now exists in “superstar” cities such as San Francisco, New York, Los Angeles, and San Jose.

London exhibits the same highly bifurcated class dynamic. Home to many of the world’s richest people, four of its boroughs also rank among the UK’s poorest and, according to British journalist David Goodhart, 27 percent of the population lives in poverty. The Financial Times’ Simon Kuper has wryly noted that that to live within 25 minutes of Soho, as he once did, “one would have to be the Queen or a homeless person.” Much the same pattern, with widening gaps between the top and the bottom of the social hierarchy, can be seen in Europe’s other leading cities, including Oslo, Amsterdam, Athens, Madrid, Oslo, Stockholm, and Vienna.

The emerging configuration of the new urban politics threatens many of the gains made over the past two decades.