The WaPo obituary for Elshtain, linked above, refers to just war theory as holding, "in simplified form, that there is a moral imperative to go into battle against forces of unambiguous evil." I'm glad that Matt Schudel, the obit's author, included the words "in simplified form."
It probably would have been better to write that 'just war doctrine' holds that there are certain conditions under which war can be considered morally justified. The most obvious example is wars of self-defense (see Art.51 of the UN Charter), although the G.W. Bush admin's often convoluted efforts to shoehorn many of its actions under the umbrella of Art.51 contributed to the skepticism with which some might view the self-defense justification. (More specifically, the invasion of Afghanistan might have been covered by Art.51; the invasion of Iraq was not.)
The more general point I want to make is that even if one disagrees with the tradition of writing about 'the just war' (which, as Schudel's obit notes, goes back to Augustine [and possibly earlier, esp. if one looks outside the 'Western' tradition]), even if one thinks that there can never, under any circumstances, be such a thing as a just war, there is no point in parading one's ignorance, as a commenter on the WaPo obituary did when he wrote:
That is a dumb remark. "Ethicist" and "just war" do not make for an oxymoron unless you think that Augustine, Grotius, and everyone else who has ever written about just-war doctrine are people who (a) don't deserve to be taken seriously, even if you disagree with them, and (b) don't deserve to be treated as writers who confronted difficult moral questions. And anyone who believes (a) or (b) or both is foolish. It is possible to be a principled pacifist, it is possible to believe there is no such thing as a just war, without at the same time being like the commenter who wrote the sentence quoted above."Ethicist" and "just war" make for an oxymoron that proves, once again, that educated does not mean intelligent.