§ 1. It is agreed that the end of a war can be good although the war itself is unjust and is waged wickedly; the end can also be evil in a just war. In either manner the war is evil. Generally, the end of war is peace, nor does anyone deny this; but they contend over it because each party endeavors to impose his own peace upon the other—one advantageous to himself and burdensome to his allies. Augustine, in book 19, chapter 12 of The City of God, observed this end in most wars:
“For whoever looks in any way upon human affairs and our common nature acknowledges with me what I say: just as there is no one who does not wish to rejoice, so there is no one who does not wish to have peace. For even those who desire wars desire nothing other than to conquer; therefore, by waging war they desire to arrive at a glorious peace. For what else is victory but the subjection of those who resist? When this has been done, there will be peace. Wars, therefore, are waged with the intention of peace, even by those who are eager to exercise martial valor through commanding and fighting. For even those who wish the peace in which they live to be disturbed do not hate peace, but desire it to be changed according to their own judgment. Therefore they do not will that peace should not exist, but that it should be the peace they will.”
No one thinks otherwise: wise men wage war for the sake of peace and sustain labor by the hope of repose. Thus it was also rightly said:
εἰρήνης ὁ πόλεμος πρύτανις.
War is the fosterer of peace. Cicero likewise commands that war be undertaken in such a way that nothing other than peace may appear to have been sought. For the courage to finish a war ought to serve peace.
§ 2. A war whose end is not right, if it is otherwise just—as when the Romans assist the Greeks in appearance but in intention destine the sovereignty of Macedonia for themselves—is indeed just if the cause of the Athenians is just; nevertheless, desire mingled with virtue makes the war evil and makes it be waged badly. For the advantage of the allies was not so much set before the greed of the Romans as was dominion. Princes, tribunes, and soldiers also sin by no means slightly in this place when, although they have a just cause for waging war, they nevertheless indulge their own hatred and neglect the public advantages.
First, indeed, they sin against charity when they exact deserved penalties from love of vengeance, not from zeal for justice. From this arise cruelty against bodies, burnings, and insults. Rude spirits do not weigh this, but wage war when embittered by mutual rivalry or by disasters.
Second, although they sin, they are nevertheless not bound to restore the losses, because they inflicted them deservedly, though not in a lawful manner.
Third, a man who, in an otherwise just war, inflicted evils upon the subjects of the prince who declared the just war will be bound to restitution.