To begin, we are conducting “defense at a distance” in Afghanistan, fighting the terrorists there so they cannot reconstitute themselves and gravely threaten us at home, as on Sept. 11, 2001. U.S. and NATO withdrawal seems nearly certain to lead to Karzai’s government falling, with the Taliban re-establishing control and inviting al-Qaida back to Afghanistan as partners. At that point, Afghanistan would again be a base for international terrorism, as we experienced on 9/11, precisely the reasons we overthrew the Taliban. And, tragically, we will have given up all we sacrificed to prevent just such a recurrence of the terrorist threat.

Second, we now recognize an added strategic threat if the Taliban retake control in Kabul, namely the increased likelihood that Pakistani Taliban and other radicals could seize control in that country. That would mean both another base for global terror attacks and also Pakistan’s substantial arsenal of nuclear weapons falling into terrorist hands, including those in Iran. Terrorists would have access to nuclear weapons they could detonate in cities around the world, rendering decades of counterproliferation efforts meaningless.

These are the strategic interests in defeating the Taliban that justify our leaving forces in Afghanistan and continuing active military operations against them for as long as it takes. This is not the same as “nation building,” which rarely works in practice and which is also truly unpopular with American voters, who see it as a gravy train for ungrateful foreigners. We are not in Afghanistan to benefit the Afghans, but to benefit ourselves.