The vitality of New York and Bangalore doesn't mean that all cities will succeed. In 1950, Detroit was America's fifth-largest city and had 1.85 million people. In 2008, it had 777 thousand people, less than half its former size, and was continuing to lose population steadily. Eight of the ten largest American cities in 1950 have lost at least a fifth of their population since then. The failure of Detroit and so many other industrial towns doesn't reflect any weakness of cities as a whole, but rather the sterility of those cities that lost touch with the essential ingredients of urban reinvention.
Cities thrive when they have many small firms and skilled citizens. Detroit was once a buzzing beehive of small-scale interconnected inventors--Henry Ford was just one among many gifted entrepreneurs. But the extravagant success of Ford's big idea destroyed that older, innovative city. Detroit's twentieth-century growth brought hundreds of thousands of less-well-educated workers to vast factories, which became fortresses apart from the city and the world. While industrial diversity, entrepreneurship, and education lead to innovation, the Detroit model led to urban decline. The age of the industrial city is over, at least in the West.
Triumph of the City, pp.8-9