As always, Agrarian, Kolokotronis, FormerLib, and others have expanded on the topic with great insights on the Orthodox phronema. Much obliged.
Anger always clouds our soul, even if it is "justified." That cloud obstructs God's light, and leaves us in the dark (passion), separated from Him. For that reason, anger is always sin.
Wars, whether "just" or unjust, are acts of anger and never of mercy or compassion. It is a product of our fallen nature, as Agrarian, points out, and as such it cannot be just. For we are all sinners, and fighting sin with sin is not just. Two negatives don't make a positive.
Western Christian concepts are different because of +Augustine's teaching of the "just" war as a last resort. This is characteristic of the juridical theology that prevailed in that region. Justifying violence in extremis opens a window to justifying sin as a last resort. As Agrarian points out, we are forced to defend ourselves because the fallen world forces it upon us, but we must never confuse that with righteousness or justice.
From Kosta50:
Wars, whether "just" or unjust,
Gentlemen(?), you've convinced me that we simply are not using the word "just" to mean the same thing. Indeed, I have always thought the term "Just War" was a regrettable choice of words ... it implies that somehow this war is good, and that war is bad. In fact all wars are bad. Sometimes, doing nothing is worse that resorting to war. Hence some wars are necessary, or inevitable or the fallen world forces it upon us. "Just" war theory is a philosophical tool for determining when that has happened, and how we are to conduct ourselves during the war, and how we are to determine that the war is or should be ended. (I would note that the list of wars, throughout human history, that has been "Just" from cause to completion is extremely short. It may well have zero entries.)
All of the above brings us back to the subject of Anger. We Catholics list it as one of the Seven Deadly Sins. And for good reason. " Anger always clouds our soul" and any decision thus made is made to a greater or lesser extent apart from the Grace of God. This may include a decision to go to war. As Agrarian points out, we are forced to defend ourselves because the fallen world forces it upon us, but that raises a very troubling issue. If any decision to go to war, and any killing in the course of that war is necessarily a sin we shouldn't do it. Ever. Under any circumstances. Even if the fallen world should try to force it upon us. We should indeed prefer to die than to commit a sin. Some things follow from this principle. For example, we should not prepare to engage in war either, lest a sin of anger should lead to a further sin of (multiple) murder. Such preparation would be a near occasion of sin (whether of a nation or an individual preparing to use lethal force in self defense), given our susceptibility to anger.