If nothing else, Detroit's bankruptcy marks the symbolic closure of an era when heavy industry dominated the American economy and, through its factories, the United States dominated the world. We think of our time as a period of wrenching change, but it's not in the same league with the tumultuous transformations of the late 19th and early 20th centuries. In these turbulent decades, the country went from a predominantly rural society of farmers and small businesses to an urban nation of massive enterprises and crowded cities.

In 1870, three-quarters of the population was rural; by 1910, that was barely half. In 1870, there were no cities with more than 1 million people and only two with more than 500,000. By 1910, there were three with more than a million and five between 500,000 and 1 million. The rush to industrialize catapulted Chicago, Cleveland, Buffalo, Pittsburgh and St. Louis into major economic centers, as the nation became dotted with steel mills and industrial plants. Detroit was a relative late-comer, emerging as the car-making hub between 1900 and 1930. Its population exploded from 286,000 to almost 1.6 million.

The great irony of Detroit's bankruptcy is that it seems to suggest the obsolescence of central cities when just the opposite is true. As economist Edward Glaeser of Harvard notes, many cities have undergone a renaissance: Boston, New York, Philadelphia, Seattle, San Francisco and others. All have stubborn concentrations of poverty; but many have benefited from gentrification and stronger job markets. High energy costs, a backlash against commuting, lower crime and cities' vibrancy have renewed their appeal.