Divided by geography, cursed by corruption, stunted by poverty, staggered by a growing insurgency—Afghanistan seems beyond salvation. Is it? From Somalia and the Balkans to Iraq, the U.S. military has been embroiled in conflicts that reflect an age-old debate: Can individual agency triumph over deep-seated historical, cultural, ethnic, and economic forces? Drawing on his experiences in Iraq, the commander of U.S. and NATO forces in Afghanistan, Stanley McChrystal, has his own answer to that question.

Image credit: Kate Brooks

We were there to fight, to do PT, to eat, to sleep, then to fight again. There was no big-screen TV or other diversion in the barracks. It was a world of concrete, plywood, and gun oil, and it was...