President Obama is considering two strategies for Afghanistan: sending in as many as 40,000 more troops to wage a full-blown counterinsurgency war (COIN in Army parlance), as General Stanley McChrystal, the top U.S. commander in Afghanistan, has recommended, or keeping the number of troops at the current level of about 68,000 to wage a more limited, counterterrorist effort aimed at al Qaeda and, to a lesser degree, the Taliban.

There is a third option: End our military occupation and leave Afghanistan to the Afghans. Let them deal with al-Qaeda and the Taliban.

To begin, 40,000 more troops, which would bring the combined U.S. and NATO force to 140,000, wouldnt be enough to conduct an effective counterinsurgency. The historical standard for counterinsurgency is 20 troops per 1,000 civilians. This is the standard recognized in the COIN manual written in large part by General David Petraeus, now head of U.S. Central Command and McChrystals superior officer. The population of Afghanistan is more than 32 million. An effective counterinsurgency would require 640,000 troopsmore than the entire U.S. Army active-duty force (548,000) and nearly the combined total of the active-duty army and Marine Corps (749,000).

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