Did you realize that another title given to St. Thomas Aquinas is that of the Common Doctor? That was the sobriquet that Blessed Pope John XXIII bestowed upon him when he addressed a Thomistic Conference back in September of 1960. Regarding Aquinas he writes,
His teaching was, more than any other, fully in keeping with the truths that God has revealed, with the writings of the Holy Fathers, and with the principles of right reason and therefore Holy Church has adopted it as her own, and has given the name of common or universal teacher to its author.
So you should be very interested in much of what the Angelic Doctor has to say on every subject under the sun. His writings are so voluminous that if he hasn't weighed in on a particular subject, it probably didn't exist at the time.
But war existed, see, and here then is an excerpt of his thoughts, which are indeed the Churches' thoughts, on that interesting and troubling subject of war. You will find them to be grounded in reality, because Aquinas, as Jacques Maritain says, is "the greatest master in realism—an integral realism, as aware of the reality of the spirit as well as of the body—who ever lived."
QUESTION XL.
OF WAR.
Article I.—Is it always a sin to go to war?
R. There are three requisites for a war to be just. The first thing is the authority of the prince by whose command the war is to be waged. It does not belong to a private person to start a war, for he can prosecute his claim in the court of his superior. In like manner the mustering of the people, that has to be done in wars, does not belong to a private person. But since the care of the commonwealth is entrusted to princes, to them belongs the protection of the common weal of the city, kingdom, or province subject to them. And as they lawfully defend it with the material sword against inward disturbances by punishing malefactors, so it belongs to them also to protect the commonwealth from enemies without by the sword of war. The second requisite is a just cause, so that they who are assailed should deserve to be assailed for some fault that they have committed.
Hence it is no justification for an enterprise of violence commenced by private individuals in a civilized State, to call it a war. Every State is bound to suppress private war within the limits of its own jurisdiction; as also to take away all pretext for such war by due redress of wrongs.
Hence Augustine says: "Just wars are usually denned as those which avenge injuries, in cases where a nation or city has to be chastised for having either neglected to punish the wicked doings of its people, or neglected to restore what has been wrongfully taken away." The third thing requisite is a right intention of promoting good or avoiding evil. For Augustine says: "Eagerness to hurt, bloodthirsty desire of revenge, an untamed and unforgiving temper, ferocity in renewing the struggle, lust of empire,—these and the like excesses are justly blamed in war."
§ i. To the objection from the text that "all that take the sword shall perish with the sword," it is to be said, as Augustine says, that "he takes the sword, who without either command or grant of any superior or lawful authority, arms himself to shed the blood of another." But he who uses the sword by the authority of a prince or judge (if he is a private person), or out of zeal for justice, and by the authority of God (if he is a public person), does not take the sword of himself, but uses it as committed to him by another.
§ 2. To the objection from the text, "I say to you not to resist evil," it is to be said, as Augustine says, that such precepts are always to be observed "in readiness of heart," so that a man be ever ready not to resist, if there be occasion for non-resistance. But sometimes he must take another course in view of the common good, or even in view of those with whom he fights.
Augustine says: "He is the better for being overcome, from whom the license of wrong-doing is snatched away: for there is no greater unhappiness than the happiness of sinners, the nourishment of an impunity which is only granted as a punishment, and the strengthening of that domestic foe, an evil will."
Article III.—Is it lawful in war to use stratagems?
R. The end of stratagems is to deceive the enemy. Now there are two ways of deceiving in word or deed. One way is by telling lies and breaking promises, and no one ought to deceive the enemy in this way; for "there are certain laws of war, and agreements to be observed even among enemies," as Ambrose says. In another way one may be deceived by the fact that we do not open our purpose or declare our mind to him. That we are not always bound to do. Even in sacred doctrine many things are to be concealed from unbelievers, that they may not scoff at them, according to the text: "Give not what is holy to dogs." Much more are our preparations to attack our enemies to be hidden from them. Such concealment belongs to the nature of stratagems, which it is lawful to use in just wars. Nor are such stratagems properly called frauds, nor are they inconsistent with justice, nor with a well-ordered will. For it would be an inordinate will for any one to wish nothing to be concealed from him by other people.
Article IV.—Is war lawful on feast-days?
R. The observance of feasts does not bar the taking the means even to the bodily welfare of man. Hence our Lord rebukes the Jews, saying: "Are you angry at me because I have healed the whole man on the sabbath-day?" Therefore it is that physicians may lawfully apply remedies to men on a feast-day. Much more is the good estate of the commonwealth to be maintained, whereby many murders are prevented, and countless ills both temporal and spiritual—a more important good than the bodily well-being of a single man. And therefore, for the defence of the commonwealth of the faithful, just wars may lawfully be prosecuted on feast-days, if necessity so requires: for it would be tempting God for a man to want to keep his hands from war under stress of such necessity. But when the necessity ceases, war is not lawful on feastdays.
§ 4. "And they determined in that day, saying: Whoever shall come up against us to fight on the sabbath-day, we will fight against him."
Interested in reading more? Head on over to the YIMCatholic Bookshelf. Also, for those who wish to explore this further, Catholic Answers has a Primer on Just War Doctrine.
Update: "Justice has been done," states President Obama, and just-war scholars agree.
