An American military exit from Afghanistan would not be a shot in the arm for the forces of global jihad, as many in the US seem to fear. On the contrary, it would remove the Taliban’s unifying element and unleash developments – a vicious power struggle in Afghanistan along sectarian and ethnic lines – whose significance would be largely internal or regional ... In fact, the most likely outcome of any Afghan power struggle triggered by an American withdrawal would be to formalize the present de facto partition of Afghanistan along ethnic lines – the direction in which Iraq, too, is headed ... As in Iraq, an American withdrawal would potentially unleash forces of Balkanization. That may sound disturbing, but it is probably an unstoppable consequence of the initial US invasion.
His analysis of the situation is probably tinged by disgust at the increased American aid to Pakistan even as Pakistan shelters all sorts of anti-Indian terrorist groups. But that doesn't make it any less true.
Al Qaeda in Afghanistan is broken. The non-Pushtun groups are strong enough to resist a Taliban takeover of Kabul. Mission Accomplished. Time to leave.