of the Church are the sword of the word of God, the shield of faith, the helmet of salvation, the breast-plate of justice, the darts of prayers, as the apostle teaches in Ephesians 6, and therefore Christians must not fight with swords and weapons.
I reply, first, that the apostle does not describe a war against men, but against demons, as is clear from this passage, “For we wrestle not against flesh and blood, etc.”150 Second, I say that the weapons of Christians are chiefly faith and prayers, but weapons made of iron are not unnecessary on that account, for in Exodus 17 we read that God granted victory to the Israelites against Amalek, with Moses praying and Joshua fighting, and we know that the Maccabees fought with weapons and prayers, and Augustine writes to Boniface, epistle 194 [Pseudo-Augustine 13],151 “Seize the weapons in your hands and let the prayer resonate in the ears of the Creator.” And Augustine writes to the same Boniface in epistle 205, alias 207 [189]: “Some fight against the invisible enemies by praying for you; you struggle against the visible barbarians by fighting for them.”
But, they say, war is the opposite of peace, and peace is good and an effect of charity; therefore war is evil. I reply that war is the opposite of peace in such a way that it is also a means toward peace, and this is the difference between a just and an unjust war. An unjust war is the opposite of a good peace and leads to an evil peace, and therefore such war is evil; a just war is the opposite of an evil peace and leads to a good peace, just as the wounds of the surgeon are the opposite of the ill and imperfect health of sick people, but they lead to good and perfect health as their end.
How many and what are the conditions of a just war?
The conditions of a just war are usually four according to those who discuss these matters: legitimate authority, a just cause, a good intention, and an appropriate way of proceeding. But each one must be discussed by itself.
The first condition is legitimate authority, as St. Augustine says in Contra Faustum, book 22, chapter 75: “The natural order of mortals, that is suited to peace, requires that the authority and deliberation to undertake a war reside in the prince, while the soldiers owe it to peace and common safety to execute military orders.” And reason proves the same, for if private citizens or anyone who has a superior are wronged by somebody, they can appeal to their superior and ask him for justice. But if princes are wronged by other princes, they do not have a common tribunal where they can complain, and therefore it is lawful for them to respond to public wrongs with war.
Moreover, this authority of declaring war resides, according to common opinion, in all princes and peoples who have no superior in temporal matters, which means all kings, the Republic of Venice, and similar entities, and also certain dukes and counts who are not subject to anybody in temporal matters, for those who are subject to others are not themselves heads of commonwealths but rather limbs. Note, however, that this authority is not required for a defensive war, only for an offensive one, for self-defense is lawful for anybody, not only for a prince, but also for a private citizen, while declaring war and invading the enemy are the prerogative of the supreme head.
The second condition is just cause, since a war cannot be declared without a cause, nor can it be declared simply for some crime, but only to ward off a wrong. Thus St. Augustine in question 10 in his Quaestiones in Iesum Nave says: “Just wars are usually defined as those that take revenge for a wrong done, for instance if the people or city against which war is waged neglected to give satisfaction for their people’s unjust action or neglected to return what was wrongly taken away.” The reason is that a prince is only a judge of his own subjects, and therefore he cannot punish all the crimes committed by others, but only those crimes that are detrimental to his subjects; for even if he is not an ordinary judge of other people, he is nevertheless the defender of his own, and by reason of this necessity he behaves in a certain sense as the judge of those who wronged his people, so that he can punish them with the sword.
Indeed, it must be observed that the cause for war must not be trivial or dubious, but important and certain, lest such war bring more harm than the hoped-for advantage. If in fact it is dubious, we must distinguish between prince and soldiers. The prince without a doubt commits a sin, for war is an act of punitive justice, and it is unjust to punish anybody for a reason not yet proved. Soldiers, however, do not commit a sin unless it is clear that the war is certainly unlawful, for subjects must obey their superior and must not discuss his commands; rather they must presume that their prince has a just cause, unless they clearly know the contrary. Likewise, when the guilt of a private citizen is dubious, the judge who condemns him sins, while the executioner who kills the condemned man does not, for the executioner is not bound to discuss the sentence of the judge, as Pope Boniface teaches in Liber sextus, “De regulis juris,” rule 25: “Whoever does something by order of the judge appears not to behave wrongly, since he must necessarily obey,”152 and blessed Augustine, Contra Faustum, book 22, chapter 75, says: “Thus it happens that a just man, if perhaps he is in the army of a sacrilegious king, could rightfully fight at his command preserving the order of civic peace, both when he is certain that what he is commanded to do is not against God’s precept and also when he is not certain that this is the case, for maybe the iniquity of the command makes the king guilty, but the duty to obey proves the soldier innocent.”
Note, however, that this indulgence must be applied only to those soldiers who are obligated to serve their prince when he wages war, such soldiers being his subjects and also those who, even in time of peace, receive a regular salary from the prince, but not those soldiers who come from somewhere else when a war has to be fought. In fact, those who are not obliged to serve in the army cannot enter a war with a safe conscience, unless they know that the war is just. Those, however, who do not think about this, and are ready to enter a war whether it is just or not, simply to get paid, find themselves in a state of damnation.
The third condition is good intention. Since the aim of war is peace and public tranquillity, it is not lawful to undertake a war for any other end. Hence those kings and soldiers who undertake a war either to harm somebody, or to enlarge the empire, or to show their prowess in war, or for a reason other than the common good, sin gravely, even if the authority is legitimate and the cause is just. So in the epistle to Boniface (no. 207 or 205 [189]), blessed Augustine says: “The will should want peace, only necessity should bring war, so that God may free us from the necessity and preserve us in peace. For peace is not sought in order that war might be undertaken, but a war is undertaken so that peace might be acquired. Therefore you should be peaceful even when fighting, so that by winning the war you may bring those whom you conquer into the unity of peace”; and in Contra Faustum, book 22, chapter 74: “Lust for harming, cruelty in seeking revenge, an unpacified and implacable spirit, brutality in rebelling, lust for power, and similar things are rightly condemned in war.”
But there are two things to be noted. First, since war is a means to peace, but a very serious and dangerous one, a war must not be undertaken immediately when there is cause; peace must first be sought in other less dangerous ways, such as a peaceful request to enemies for the satisfaction that they owe: Deuteronomy 20: “When thou comest nigh unto a city to fight against it, then proclaim peace unto it,”153 and blessed Augustine, epistle 207 [189] to Boniface: “The will must want peace, only necessity should bring war.”
But you will ask, if the enemy at first does not want to give satisfaction, but soon, with the war already begun, asks for peace and offers to give satisfaction, will the other be bound to desist from war? Cajetan at the entry “war” says that he is not bound to end the war when it has already begun, but he would be obliged to accept satisfaction before beginning the war. But (with the proviso of a better judgment) it seems that we must say that he who has a just cause is never bound in justice to accept satisfaction either before the beginning of the war or after, but in both cases he is bound to do so out of charity. The reason for the former is that a prince who has a just cause for war functions as judge of the other prince, who wronged him, but a judge is not bound in justice to pardon a guilty man who is condemned to death even if he offers satisfaction; nevertheless he could pardon him out of mercy, if he is the supreme judge. For example, a