Chapter I. FROM WHAT LAW DOES WAR COME?
IN this fourth and last part of this book I ask from what law does war come. To this I reply that we have a law which we call divine law, that is, the law of God.

Hence we muse consider and understand whether war is a thing condemned by this divine law. Many simple folk think it is so condemned, for the reason that in war and battle many evil things are done, and to do evil is reproved and condemned by this law of God. Hence war is not, and cannot be, in accordance with this divine law. I tell you that this argument is worthless ; for the truth is that war is not an evil thing, but is good and virtuous ; for war, by its very nature, seeks nothing other than to set wrong right, and to turn dissension to peace, in accordance with Scripture. And if in war many evil things are done, they never come from the nature of war, but from false usage ; as when a man-at-arms takes a- woman and does her shame and injury, or sets fire to a church. Such cases do not come from the nature of war itself but from false usage of battle and war, and from war wrongly conducted. We speak similarly of the virtue of justice, by which the judge must act reasonably, according to his lights ; but if a judge acts unjustly, shall we say that justice is a bad thing ? Certainly not, for wrongdoing never comes from the nature of justice but from wrong usage and interpretation, and a bad judge ; for all good things, and all virtue, come from God.

Thus we must understand that war comes from God, and not merely that He permits war, but that He has ordained it ; for God commanded a man called Joshua that he should do battle against his enemies, and advised him how he should set an ambush for the discomfiture of his enemies. Further, we say that our Lord God Himself is lord and governor of battles. And for this reason we must accept and grant that war comes from divine law, that is, the law of God : for the aim of war is to wrest peace, tranquillity and reasonableness, from him who refuses to acknowledge his wrongdoing. And if, in the waging of war, the good have to suffer for the bad, it cannot be otherwise, for, indeed, war is to be compared to a medicine. We can see how illness comes to the human body through excess of humours, and to reduce this excess the doctor gives the remedy. Very often, however, the drug affects the good humours along with the bad, for in such degree are they mingled and intermixed that it cannot be otherwise : and this is because they are so near and neighbouring, one to the other. And there is a great example of this in the Holy Scripture ; for when God wished, because of very evil sins of the flesh against nature, to destroy three cities : that is, Sodom, Gomorrah, and Zeboim, two other cities which lay near to these were burned with those mentioned above. Hence we have a clear example of how the good must sometimes suffer by reason of their evil neighbours. Thus a gardener cannot pull out all the weeds from among the good plants without plucking from the earth the good with the bad ; and thus we see very often that, for the excess and fault of one man, a whole line can be destroyed ; and of this we have an example in a certain Gigacy, who, through his sin, caused all his descendants to be thieves and robbers. A stronger example still is that through the defect of a king a kingdom will fall to ruin ; and we fmd that for the sin of David mortality spread through his kingdom.

But, notwithstanding that by these arguments I have sufficiently proved that war comes from divine law, at the same time you must understand that we have another law, which we call in Latin the law of nations, jus gentium. And it is not to be doubted that war is to be found therein, as the decretal and the civil law assert. And if you ask what is this law of nations, I reply that it is that law which covers everything which is according to reason in general. Canon law and civil law can also be called law of nations, for they set forth and specify cases according to reason, and give them fitting form, so that we may learn how things should be ordered.
But I say something still stronger : that is, that war comes from the law of nature, because everything is inclined by its nature to contradict its evil form, and its contrary, so as to preserve itself, and its being, and the qualities that belong to it. Hence war in general is justified by all laws. But we must examine more closely particular cases and other matters and the arguments that I shall put forward in various places when dealing with subjects that come later.