A good review article by Steve Coll, on why Afghanistan is important: http://www.newyorker.com/online/blog...tml#entry-more

In this war, we have two important interests: One is largely uncontroversial: The reduction of Al Qaeda to a nuisance or less. The second American interest in the war, however, is by some margin the more important and enduring one. Yet it is also a more complex subject...The United States has a deep interest in the emergence of a stable, modernizing, economically integrated, peaceful South Asia....Why does the Afghan war figure in this assessment today? The Taliban are a backward-looking threat to the near-term stability of South Asia—in Afghanistan, in Pakistan, and, as the Mumbai attacks demonstrated, occasionally in India..... these regional American interests at issue in the Afghan war are very powerful; to confirm this, consider the alternative of Pakistan’s failure at the Taliban’s hands.
Grand Strategy no less: reduce AQ's threat and keep South Asia from war.

davidbfpo