I was struck by something the mayor of Cincinnati said recently in a conversation on the Urbanophile blog, published by one of our Governing columnists, Aaron Renn. The mayor, John Cranley, essentially proclaimed that the time has come for cities to stop dreaming of regional solutions to urban problems, to stop thinking that they would be better off if they could annex the suburban territory that lies just outside their borders. Cincinnati, he said, can get along just fine without any more than the roughly 80 square miles and 300,000 people that it currently comprises. At this point in the 21st century, Cranley argued, taking on suburban territory simply gives cities new problems that they don’t need.

The mayor expanded on his ideas with me in a subsequent conversation. In the past, he told me, “You had a sentiment that urban cores need the wealth of the suburbs to have a better budget picture. People in the suburbs escaped the city to flee the problems. But that’s changing. You’re going to see cities in a better financial situation than a lot of the suburbs.”

Cranley’s assertions challenge what has been an article of faith among urban planners and good government advocates for the past hundred years. For all that time, it has been widely assumed that cities suffer in large part because they are geographically too small -- they are cut off from the affluent neighborhoods and sizable tax bases that the suburbs contain. Bring city and suburb together, the argument has always gone, and the result would be a diverse, prosperous and efficient consolidated region properly equipped to deal with the challenges of modern metropolitan life.

Yearnings for metropolitan regionalism and consolidation have existed for most of the history of the United States. Throughout the 19th century, cities and suburbs combined through the simple annexation of suburban territory into the city, a move usually agreed to by the suburbs because of their need for the water that the city could provide them. But in the 20th century, suburbs began to develop their own sources of water, and they came to regard nearby big cities as less than ideal partners, saddled with large immigrant populations, neighborhoods of extreme poverty and high-crime rates. So in most of the older metropolitan areas of the Northeast and Midwest, suburbs began to want as few ties to the larger urban entity as possible.

Despite an enormous amount of literature arguing in their favor, the number of actual urban-suburban consolidations in recent decades has been small. Indianapolis famously did it in the early 1970s, pushing city-county consolidation through without having to subject the idea to a popular vote. Louisville did it in the 1990s, creating one metropolis out of the city and all of surrounding Jefferson County. Louisville’s consolidation advocates argued from the standpoint of regional pride rather than efficiency; they pointed out to voters that by undertaking a consolidation, Louisville could advance from being the 65th largest city in the United States to the 23rd largest.

Nashville and Jacksonville also have consolidated city-county governments. Other large cities, such as Charlotte, have adopted many of the features of consolidation without joining suburbs to city in a full legal sense. But the number of cities that have proposed consolidation and failed to win voter approval for it is much larger than the number that have made the move successfully. Between 1902 and 2010, according to the urban scholar David Rusk, 105 referendums were held in the United States to consider city-county consolidation. Only 27 of these won the approval of the voters.

Still, the issue remains on the table, and the idea for regional cooperation has been prominent among urban policy scholars in the past couple of decades. Among the most effective advocates of consolidation has been Rusk, the former mayor of Albuquerque, N.M., who has argued that cities unable to include suburban territory within their borders have been condemned to deal with painful fiscal stresses and school systems that are segregated in all but the nominal sense. Rusk has touted the virtues of newer cities in the South and West that have annexed large chunks of suburban territory and have achieved higher levels of racial balance in their school systems. In his view, it is these elastic cities -- those able to grow by annexation or consolidation -- that are best equipped to meet the challenges of modern governance.

But even as this debate has proceeded, it has been propped up by an underlying assumption: that suburbs are the prize in this governmental competition, and cities are the poorly endowed suitors. It is this entrenched idea that Cranley has dared to challenge.

And there is support for Cranley’s view in some of the numbers that have been released by the Census and scoured by demographers in the past couple of years. Foremost among the sources of evidence is the book Confronting Suburban Poverty in America, published last year by the Brookings Institution.

The authors of that book, Elizabeth Kneebone and Alan Berube, presented some figures that many suburban leaders have been reluctant to confront. Among them were these: In 2011, the suburban poor outnumbered the urban poor by 3 million; in the first decade of the new century, the number of poor people in the suburbs rose by 64 percent.

None of these numbers erase the powerful fact that cities still have a higher percentage of poor people than suburbs do. Nor do they cancel out the depressing reality of dysfunctional, largely abandoned swaths of territory in some of the biggest cities in America, such as Detroit and Philadelphia. But they do suggest that urban policymakers need to think about the suburbs in more nuanced ways than they have in the past.

Just outside the border of every large American city lies inner suburbia. Some of this consists of large homes and leafy streets created before the Second World War. This part of the suburbs is economically healthy and a desirable place to live. But right next to it is a different part of inner suburbia -- small jurisdictions built for the industrial working class in the immediate postwar years. This is the suburban territory that has suffered badly in the last five years from unemployment, disinvestment and the deterioration of its housing stock. Most of the homes in this part of inner suburbia are cramped bungalows too small to attract many would-be customers in the current home-buying generation. These suburbs are almost all in fiscal trouble to some degree. When a mayor such as Cranley talks about the era of annexation being over, this is the territory he most clearly would not want to annex.

Beyond these two layers of suburbia are the exurbs, the newest communities, most of them built after about 1980, generally with good-sized homes designed for families looking for safe streets and good schools. These suburbs, like the prewar version of inner suburbia, are generally doing well. But they are far enough from the city limits -- 30 to 40 miles out, in many cases -- to make active collaboration with the central city on many issues impractical. The residents of exurbia are to a great extent people who want as little to do with the city and its problems as possible.

So the mayor of a city like Cincinnati looks out of his window and sees three different suburbias: an older, affluent one that values its long-established independence; a larger, poorer one that has relatively little to offer the city in tangible terms; and a more distant exurban one whose residents wish to leave the city behind them. He knows that of all the poor people living in Greater Cincinnati, 72 percent of them are in the suburbs outside his immediate jurisdiction. And so it is no surprise that he would conclude that the era of metropolitan regionalism is coming to an end.

If cities do make a sharp turn against consolidation and annexation, what will that do to the more modest forms of cross-border cooperation that have been gathering momentum in much of the country for the past few years? My guess is, not very much. Since the Great Recession began in earnest in America six years ago, many communities have signed on to compacts that have them providing a whole variety of services, most notably routine law enforcement and emergency medical response, on a shared basis. Governors such as Andrew Cuomo in New York and Chris Christie in New Jersey have pushed through legislation giving communities financial incentives to share services as a way of avoiding wasteful administrative duplication. This is nothing new -- governors of New Jersey have been pushing local government consolidation of all sorts for the past generation -- but in the current climate of local government austerity, the willingness to share has moved further than it it had done in the past.

Most of those accomplishments have occurred at a small-town level, however. The past few years have seen no revival of enthusiasm for consolidation or annexation involving big cities and their suburbs. Mayor Cranley offers a simple but compelling reason why: Cities don’t feel jealous of suburban affluence at this point in their history; they don’t feel that a suburban connection offers them much that they can’t achieve better on their own.

In other words, the era of cities scheming to join forces with the suburbs next to them has already come to an end. I haven’t heard any other big-city mayors say this directly, but I wouldn’t be surprised if quite a few of them are thinking it. And the consequences for urban government in the next generation are likely to be substantial.