Less than two years ago, Sunbelt-and-sprawl advocate Joel Kotkin wrote in The Wall Street Journal that the future of American urbanism wasn’t in the “elite cities,” such as New York, Boston and San Francisco, but in “younger, more affordable and less self-regarding places.” His examples included Las Vegas.

What a short future that was. Las Vegas is now a mess, as an economy built on risky mortgage lending, speculative building and casino gambling implodes. Vegas now has the highest foreclosure rate in the country — almost seven times the national average.

Las Vegas is certainly affordable now. House prices there have fallen 55 percent since peaking in August 2006. Of course, these homes are only affordable if you have a job. The unemployment rate there now exceeds 13 percent (like Rhode Island’s until just the other day). Last year, the population of Clark County, which is mostly Las Vegas, actually fell.

The main economic engine, casinos, is reeling. Tourism is off 6 percent from last year, and the convention business is down a third. The high-rollers are rolling no more. Luxury hotel rooms are approaching “roadside motel prices,” as Business Week put it.

It’s too bad that serious business people buy into the boom-city mentality pushed by Mr. Kotkin and other peddlers of mindless growth. The Las Vegas Strip is now quaking this month as MGM Mirage prepares to open its new CityCenter resort. The $8.5 billion project will add another casino, 4,800 hotel rooms and 2,400 condominium units to the city’s bloated supply.

Las Vegas already has gigantic new condo towers with but a handful of occupants. (Real-estate professionals call these “see-through buildings,” because they are so empty, there’s nothing inside to stop one from seeing to the other side.)

Speaking of which, many such projects would not have been started had developers not relied on Federal Housing Administration loans. Itself in trouble, the FHA has been trying to tighten its requirements on condominium loans. It has proposed requiring that an entire project meet FHA approval before unit-buyers can get a government-guaranteed loan. It wants to limit FHA loans to no more 30 percent of a condo development’s units. And it wants at least half the units sold before it will insure a buyer’s mortgage.

These rather common-sense rules were set to go into effect on Oct. 1. But lenders and builders have complained about them, so the effort to better regulate FHA condo loans is on hold.

The lesson here is that economies can’t be sustained by real-estate speculation and borrowing — and that gambling as economic development is no sure bet. Also, it’s not a good idea to dismiss old cities with educated populations as effete has-beens. They may not boom much, but they do well over the long haul.