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Handing out guns in Afghanistan has been risky business through the ages, yet arming Afghan village defense forces is central to Army Gen. David H. Petraeus' strategy against the Taliban. The commander of U.S. and NATO forces in Afghanistan is taking a page out of the counterinsurgency manual he drafted for Iraq, where he successfully coaxed Sunni Arab fighters into government-allied local defense units. But that doesn't mean it will work to hire local hands in the treacherous terrain of Afghanistan, where several foreign powers have tried and failed to control the gunmen. Americans often are accused of having short memories,...