You may have thought the Olympics were about athletic achievement, national pride, or global cooperation. Actually, they're about urban planning.

At least that's the impression you might get from the debate over which city should host the 2012 games, a battle that ended Wednesday with London taking the prize (and then vanished from public discussion Thursday, as terrorist attacks in the same city seized our attention). Paris promised to undertake new urban renewal projects. New York offered a brand new stadium in Manhattan and, when that fell through, a brand new stadium in Queens. London won with a proposal to "regenerate" the city's East End, a plan that's expected to cost at least $15.8 billion.

Visit the London 2012 website, and you'll find enough promises to fuel a dozen New Hampshire primaries: 12,000 new jobs! 9,000 new homes! With the Olympics, the site argues, "the regeneration would be quicker and on a far larger scale; it would mean great new sports facilities for the whole community....London would also have the one of the largest new urban parks that Europe has seen for two centuries incorporating many revitalised canals and rivers. Finally, hosting the Paralympics, and its thousands of athletes, would improve the way the city and its infrastructure functions for all people with disabilities."

These aren't just offerings to the Olympic committee. They're supposed to silence domestic critics as well. Like other highly touted mega-events, the Olympics frequently cost more in public spending than they produce in new revenue, a fact that might dampen local support. So the boosters' backup argument involves the purported long-term advantages for the city. The Greek government shelled out approximately $12 billion for the 2002 Olympics in Athens—more than twice the initial estimate—and the spectators' Euros weren't nearly enough to make up the difference. Some Greeks did pretty well, especially in the construction industry, but the rest of the country was stuck with a steep bill. Still, when the Associated Press went searching for a benefit beneath the economic disaster, it managed to conclude that the games were "a reason and deadline to fix the messy and ill-planned urban sprawl under the Acropolis." That, and the city got some new public transit.

Britons may feel wary accepting such promises from a government whose best-known urban improvement project is the Millennium Dome, the most infamous white elephant in Europe. (Built to mark the year 2000, the Greenwich money pit received barely half the expected visitors and became an immense political embarrassment.) But even if the rosy predictions turned out to be true, there would be something puzzling about them. Let's suppose, just for the sake of argument, that hosting the Olympics is worth the price tag, that it will create more jobs than it destroys, and that the money involved is better spent on the government's projects than on whatever the individual taxpayers would have bought. You still have to wonder: If the games had gone to Paris instead, is there any reason London still couldn't give itself a new park, a new stadium, and handicap-accessible facilities? If publicly financed "regeneration" is such a great thing, why does it require a sports event to unleash it? Boosters love to call the Olympics an "opportunity"—but how are they an opportunity to do something the government could do anytime?

They're an opportunity because they come with their own momentum. A city tapped to host the Olympics is like a nation-state operating under wartime conditions: It has a license to do things that might otherwise be blocked. While the U.K. was still campaigning to host the event, Martin Samuel of the London Times observed that the London Development Agency was dithering on a plan to fully compensate the small businesses that would be displaced by the new facilities. (Such problems eventually led the Marshgate Lane Business Group to formally oppose London's bid for the games.) "Right now," Samuel wrote, "there remains a battle for hearts and minds, but if London wins, the hoopla will begin and the LDA will be able compulsorily to purchase land without respect for local sensibilities." Industrial policy always has winners and losers. The Olympics are an "opportunity" for the victors to claim their winnings.

The Athens experience might seem to cut against that: There was plenty of cronyism in awarding the construction contracts, but the builders' plans were sometimes held up by local opposition in the courts. (They also had an unfortunate habit of stumbling on archeological treasures while they were building, creating still more delays.) But as the deadline neared, construction went into overdrive; budget limits were forgotten, safety standards were ignored, many workers died, and the Olympic Village arrived as planned. The government then swept up anyone who might look unsightly or dangerous, from homeless people to asylum-seekers and refugees.

Of course, there's more to hosting the Olympics than government spending and grand urban makeovers. You get to be the international capital of nationalist furor for a few weeks, and you get a security apparatus so tight it makes an airport look like a free country. Everything you need to be a world-class city!

The historian Nigel Spivey has described the ancient Olympics as "war minus the shooting." When the U.S.-Soviet rivalry defined the games, the modern Olympics were essentially the same thing. But even in the absence of a grand geopolitical rivalry, the Olympics have something in common with warfare. They both strengthen the state.