The classic defense of our involvement in Afghanistan is that we need to make sure that Afghanistan never again becomes a sanctuary for al-Qaeda or other enemies of the United States. Ungoverned spaces attract terrorists, especially when they’re in bad neighborhoods. (See: Pakistan.)
That is strategy. The classic defense of our tactics is that we are fighting a counterinsurgency according to best practices, providing security to the people of Afghanistan so that they can choose to support their electedgovernment rather than the insurgency. Everything our military does inAfghanistan is aimed at that goal. We are trying to train the Afghansecurity forces to the point where they can take over from us, just as the Iraqi security forces mainly have, and we can go home.