An interesting article by Michael Walzer on 'just war theory' (thanks to Ektopos for the link). I didn't disagree with much, but that's because the essay is very general. As I've noted before, I think that properly speaking 'just war theory' in the traditional (e.g., Thomistic) sense is a much more precise theory than people would like it to be. It essentially just says that someone authorized to protect a people from being harmed by their enemies can (if he is authorized to do it, i.e., assuming that the responsibility for protection isn't divided up) take active measures to protect them from being harmed by external enemies without violating justice or charity. (It gets a bit more complicated when the responsibilities of protection are divided up, but mutatis mutandis it's along the same lines in that case.) It is a theory about warfare not in the vague, general sense in which we use it, but in the sense of the actual war-activities of someone authorized to wage war. It barely extends even to the soldiers who actually fight, in an attenuated way through the ethics of obedience. It does not extend to civilians at all; their activities in war are governed by an entirely different part of the ethical theory. While it does give to the war-wager considerable room to maneuver, it also imposes sharp limits. For instance, you can feint but not lie: i.e., you can set things up so that your opponents are misled, but you cannot actually lie to them (violation of truth is violation of justice and charity; all the traditional just war theorists even up into the early modern era agree on this). It is unjust and uncharitable for bishops to fight, or for anyone to fight on high holy days - but, oh, yeah, this is because traditional 'just war theory' is explicitly and unflinchingly a Christian doctrine.
In Aquinas, there is no distinction, and can be no distinction, between jus ad bellum and jus in bello: what makes warring just or unjust is exactly the same in both. The Spanish scholastics distinguish between the two because they are interested not merely in the justice or injustice itself but in the practical reasoning, and the details of the practical reasoning of going to war is at a slightly different level than that of actually fighting the war. While I think we must allow for the latter difference, I am certain that Aquinas is right: there is no fundamental distinction between the justice of going to war and the justice of fighting in a war: it's just useful for practical purposes sometimes to distinguish them. And I think, contrary to Walzer's view, the traditional just war theory requires that we look at war as a very heavy-duty police action - messier, more complicated, less rule-governed, and less likely to end up in a but it is a different, and more terrible, manifestation of exactly the same civic protective authority. Walzer is right that it is different from domestic actions of the police, but it is the other side of the same coin.