WHEN I moved to Washington, D.C., in 2002, you could sense that the nation’s capital had turned a corner after decades of decline. But the Washington of 10 years ago still looked basically like the city that had been scarred by riots in the 1960s and then emptied by white flight, with a prosperous northwest divided from a blighted south and east, and frontiers of gentrification that weren’t that many blocks from the Capitol itself.

No doubt there were boomtowns in the 19th-century Wild West that changed faster than D.C. did over the ensuing decade. But the changes to Washington have been staggering to watch. High-rises have leaped up, office buildings have risen, neighborhoods have been transformed. Streets once deserted after dusk are now crowded with restaurants and bars. A luxurious waterfront area is taking shape around the stadium that the playoff-bound Nationals call home. Million-dollar listings abound in neighborhoods that 10 years ago were transitional at best.

And that’s just inside the District proper. Cross the bridges into Virginia or shoot north into Maryland, and you’ll find concentrations of wealth greater than in the richest counties around New York and Los Angeles and San Francisco. Last week, new census data revealed that 7 of the 10 richest American counties in 2011 were in the Washington, D.C., region. Fairfax, Loudoun and Arlington Counties, all in Northern Virginia, have higher median incomes than every other county in the United States.

Whence comes this wealth? Mostly from Washington’s one major industry: the federal government. Not from direct federal employment, which has risen only modestly of late, but from the growing armies of lobbyists and lawyers, contractors and consultants, who make their living advising and influencing and facilitating the public sector’s work.

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