George Weigel has a good essay in a recent issue of First Things summarizing and applying the just war tradition. It’s worth reading the whole, but especially his argument in response to those who argue that just war theory censures pre-emptive wars because war can only be the last resort:

The charge that U.S. military action after September 11 was morally dubious because all other possible means of redress had not been tried and found wanting misreads the nature of terrorist organizations and networks. The “last” in last resort can mean “only,” in circumstances where there is plausible reason to believe that nonmilitary actions are unavailable or unavailing.