To anyone steeped in the thousand-year history of Anglo-French enmity — that bitter struggle over power, influence, and the edibility of snails — the highlight of France’s presidential election campaign was surely the speech that the center-right candidate, Nicolas Sarkozy, who is now the very precarious front-runner, gave this year in London.

Standing in the heart of London’s financial district, Mr. Sarkozy heaped compliments upon his country’s historic enemy. The British capital was, he said, a “town that seems more and more prosperous and dynamic every time I come here.” More important, it had become “one of the great French cities.” He understood, furthermore, that hundreds of thousands of Frenchmen had moved to Britain because “they are risk-takers, and ‘risk’ is a bad word” in France. With distinctly un-English passion — some things never change — he pleaded with them:

“Come home, because together we will make France a great country where everything will be possible, where fathers won’t fear for the future of their children, and where everyone will be able to make their plans come true, and be responsible for their own destiny.”

Unfortunately, it seems that even a Sarkozy victory in the final round of voting on Sunday won’t persuade all of the 2 million-plus French exiles to go home. Asked by a French polling company, TNS Sofres, “Are you satisfied with your life abroad?” 93% of French emigres surveyed recently said “yes.” Asked, “When do you expect to return to France?” 25% answered “never.”

To Americans, who’ve become used to the idea that people take jobs far from home, that people move to places where the economy is better, and that consequently some cities shrink like St. Louis while others grow such as Los Angeles, there is nothing odd about the fact that the French now vote with their feet.

There are better-paying jobs in London, taxes are lower in London, the economy grows faster in London: C’est la vie — and tough luck for Paris. But Europeans have not, historically, been quite so mobile. Even a decade ago, tradition and sentiment kept people at home; legal and linguistic barriers made it hard to move, even if they wanted to go.

Thanks to the European Union, which has opened borders and eliminated employment barriers, it is now not only possible to move, it is downright easy. And not only for the French: Something like a million Poles have left home since Poland joined the European Union in 2004, largely for England and Ireland.

Unlike France, Poland is booming. But as in France, high taxes and complex regulations mean that jobs for young Poles are still too scarce and badly paid. Abroad, young Poles earn more and are treated better.

When they come back, if they come back, they ‘ll demand no less. The plumbers in Warsaw already expect to be paid something remarkably close to what plumbers are paid in Berlin — that is, if you can find a plumber in Warsaw at all.

All of this is, of course, precisely what previous generations of European politicians have feared. For the past decade, French, German, and other European leaders have tried to unify European tax laws and regulations, the better to “even out the playing field” — or, depending on your point of view, to make life equally difficult everywhere. The emigration patterns of the past decade — and the past five years in particular — prove that that effort has failed. Mr. Sarkozy’s election campaign, if successful, might put the final nail in the coffin.

The political and economic consequences of this new mobility could be quite profound. Countries such as Poland and France may soon be forced to scrap those regulations and taxes that hamper employment, however much the French unions and the Polish bureaucracy want to keep them: If they don’t, their young people won’t come home.

Leaders in those countries may also have to alter their rhetoric. Mr. Sarkozy’s Socialist opponent, Segolene Royal, now uses words such as “entrepreneurship” at least some of the time, too.

Down the road, there could be cultural consequences as well. A few weeks ago, I wrote about the European Union’s failure to create anything resembling a meaningful European “Idea.” Almost by accident, the European Union may have created a new kind of European citizen instead: mobile, English-speaking, Internet-using, perhaps with the same nostalgia for Krakow or Dijon that first-generation New Yorkers feel for Missouri or Mississippi but nevertheless willing to live pretty much anywhere. Mr. Sarkozy is the first European politician to appeal directly to these new Europeans. Even if he loses, he probably won’t be the last.