§ 1. The first cause, and the most just of all, exists if an unjust war is brought upon one. But it is brought unjustly in two ways. First, when war is declared upon the innocent, as the Moabites declared unjust wars upon the Jews, and likewise Antiochus and others—with such men, alas, history is full. In the second way, when a war was just at its beginning but is rendered unjust by satisfaction not being accepted. For example, the Venetians seize an Ottoman ship contrary to a treaty; the Turk declares war; the Venetians restore the ship, merchandise, passengers, and all losses, and promise to make satisfaction for the injured honor and authority of the emperor, either according to his own judgment if he commands equitable terms, or according to that of arbitrators if he wishes to appoint them. But if he moves war absolutely and wishes a most noble state to surrender itself to him, they will rightly resist with all their strength, because the sin is not so great that they ought to deliver themselves to a most cruel enemy and, together with their liberty, ruin themselves also in religion.
This cause is not only just but also necessary. For the prince who does not defend the state sins against justice just as much as he who invades the possessions of another. Therefore, against one who inflicts harm, defense is not only just but necessary. Here I pronounce boldly: he who desires peace should prepare war. Here especially has place that saying of Isocrates:
Οὐκ ἀθυμεῖν δεῖ τοὺς ὑπὲρ τῶν δικαίων κινδυνεύειν μέλλοντας, ἀλλὰ πολὺ μᾶλλον τοὺς ὑβρίζοντας.
Those who are about to incur danger for a just cause ought not to be downcast, but rather those who inflict injury. Chilon used to say that this was the difference between a good prince and a tyrant, and that they were recognized from the matter about which they contended: the tyrant broods over another’s possessions; the prince defends his own.
§ 2. The second cause is the detention of things taken away. For just as citizens, who have a judge, when something has been taken away, recover it at law and appoint a day for the adversary, so a state, when it has sent ambassadors to demand back its possessions in vain, prepares and declares war. Moreover, the cause of demanding back possessions is various and as diverse as it is within a city. For something may have been taken away by theft or robbery; what had been deposited may not have been returned; justice may have been denied to citizens; or an inheritance may have been withheld.
A war is just when an enemy carries off and drives away the possessions of neighboring lands by plundering. The Roman people waged such a war with the Illyrians and Gauls, and afterward with barbarian peoples. “For things which they cannot possess together, they fight in unhappy want; laborious wars seek this peace, and glorious victory obtains it.” For the great and wealthy are attacked for this reason: the wind overturns the oak because it is laden with acorns and foliage; willows are exempt. Thus the Britons were safer for a long time because they denied that there was an ounce of gold among them.
War is also waged when justice is denied to citizens or merchants are detained. Among the northern peoples there were many such cases in ancient times, and atrocious battles. When an inheritance is divided unjustly, there is the case against Jugurtha, who through adoption had received with Adherbal the right to divide the kingdom and had corrupted Roman ambassadors and commanders with money. War was waged for this reason, because he had joined parricide to it.
§ 3. In these causes, not only the magnitude of the loss must be considered, for sometimes it is not worthy of war, but also the design of enemies who are seeking wars. If their first injuries are not opposed, they will be bolder for second and third injuries; and then, after greater losses have been received and the spirits of your men weakened, it will be necessary to fight men who are more confident.
§ 4. War is also frequently undertaken for the sake of vengeance, when the enemy has injured one in any matter whatsoever. It is not waged so that things may be recovered, since they either have not been taken away or have been consumed, but so that the wicked may be punished and the state made safer by this means. No one ought indeed to furnish vengeance for himself; nevertheless, a state ought not to leave its own injuries unavenged without cause, whether they are inflicted by private persons or by another state. Because it possesses the sword for vengeance upon evildoers, it ought therefore to use it with reason.
§ 5. War can also be waged when religion is attacked and God is blasphemed. This happens in two ways. The first is when foreigners live wickedly and afflict God with insults but nevertheless do not harm others. The second is when they attempt by deceit, fraud, and violence to draw others into the same sins, and actually do so.
If they are wicked and blasphemous only toward themselves, it is not lawful to wage war against them for that cause alone, because one state is not the judge of another state, while it belongs to a judge to punish sins. Nevertheless, by the express admonition and command of God they can make war. Thus Joshua killed the Canaanites by God’s command because their iniquities had now been completed. They did not touch the Moabites and Edomites, who were not much better, because they had no command to punish their crimes.
§ 6. But when by force or fraud they attempt to bring their vices into a state, they also give a just occasion for war. Thus the Maccabees waged most just wars against Antiochus and others who compelled men by force to idolatry.
§ 7. This is so not only when they solicit the minds of subjects to crimes by violence and armed force, but also when they do so by fraud and blandishments. When Moses had occupied Bashan and the neighboring regions, the Moabites and Midianites, seeing themselves unequal in war, received the Israelites hospitably as brothers, gave them gifts, and sent their daughters to take care of the guests, so that under the appearance of friendship and of marriages to be contracted they might entice them to fornication and adulteries, and then, once they had been weakened by lustful love, to idolatry. When this had been done, as Balaam had conjectured, God, being offended, would either destroy them utterly or at least, when they had been deprived of heavenly aid, offer them to their enemies to be conquered.
And the deceit succeeded, Numbers 25: “Now at that time Israel abode in Shittim, and the people committed fornication with the daughters of Moab, who called them to their sacrifices. But they ate and adored their gods. And Israel was initiated into Baal-peor; and the Lord was angry and said to Moses: ‘Take all the princes of the people and hang them upon gibbets before the sun, that my wrath may be turned away from Israel.’ And Moses said to the judges of Israel: ‘Let each one kill his neighbors who were initiated into Baal-peor.’”
For this crime a severe vengeance is exacted in chapter 31: “And the Lord spoke to Moses, saying: ‘First avenge the children of Israel upon the Midianites, and then you shall be gathered to your people.’” And immediately Moses said: “‘Arm men from among you for battle, who can exact the vengeance of the Lord from the Midianites. Let a thousand men from each tribe be chosen from Israel to be sent to war.’ And they gave a thousand from each tribe, that is, twelve thousand men equipped for battle. Moses sent them with Phinehas, son of Eleazar the priest, and delivered to him the holy vessels and the trumpets for sounding. And when they had fought against the Midianites and conquered them, they killed every male and their kings, Evi, Rekem, Zur, Hur, and Reba, the five princes of the nation. They also killed Balaam son of Beor with the sword. And they captured their women and little children, all their cattle, and all their furniture; whatever they could possess they plundered. They consumed with flame both cities and villages and castles. And they took the spoil and all that they had captured, both from men and beasts, and brought it to Moses and Eleazar the priest and to the whole multitude of the children of Israel; but the remaining utensils they carried to the camp in the plains of Moab, beside the Jordan opposite Jericho.
“And Moses and Eleazar the priest and all the princes of the assembly went out to meet them outside the camp. And Moses, being angry with the princes of the army, the tribunes and centurions who had returned from the war, said: ‘Why did you spare the women? Are not these the women who deceived the children of Israel at Balaam’s suggestion and caused you to transgress against the Lord in the sin of Peor, whence the people were struck? Therefore kill all who are of the male sex, even among the little children, and slaughter the women who have known men in intercourse.’”
God decreed this war beforehand, Numbers 25:17: “And the Lord spoke to Moses, saying: ‘Let the Midianites feel you as enemies, and strike them, because they too acted as enemies against you and deceived you by snares through the idol of Peor and through Cozbi, daughter of the prince of Midian, their sister, who was struck on the day of the plague for the sacrilege of Peor.’”
§ 8. Not only must a war be just; for it to be waged rightly, a wise man ought to grieve that a just cause of wars is given. For those who eagerly seize even a just cause and rejoice that an occasion has been given seek anything rather than justice. Both Romans and Carthaginians were disposed in this way before the Second Punic War. For when the ambassador said that he carried peace and war, the Carthaginians ordered him to give whichever he preferred, and he poured war from the fold of his garment, not without terror. Augustus acted better, for, as Suetonius writes in chapter 20, he brought war upon no nation without just and necessary causes. For he watched over the empire not to enlarge but to protect it. Therefore, he was unwilling to bring war upon those at peace and grieved when it was brought upon him.
§ 9. A war is also just against those who have assisted an enemy in an unjust war. For that cause the Romans frequently subdued peoples, and particularly the Picentes and Sallentines, because they had borne arms for the Tarentines. They decreed war against Philip of Macedon because he had allied himself by treaty with Hannibal while the latter held power in Italy, although the prayers of the Athenians also impelled them to it. War was also brought upon the Aetolians because they had stood by Antiochus. For the same cause the Histrians were subjugated because they had assisted the Aetolians. The Gallograeci, who were said to have been in Antiochus’s camp, were in the same position; but the senate did not approve the cause of the war, wherefore a triumph was denied even to the victorious Manlius. Thus many peoples followed the ruin of the Syrian War. The contagion of the Second Macedonian War drew in the Illyrians; and while the Roman pursued all who were privy to it, as though by a chain, he subjected the world to himself, with peoples either furnishing causes or the Roman seeking them out.
But for this war, in which an enemy’s σύμμαχοι, or allies, are attacked, to be just, two things are required. First, they must truly have assisted, not merely favored, the enemy. For if the Spartans are enemies of the Athenians, the Thebans are not therefore also bound to withdraw from friendship with the Athenians. Since they are free, they can love those whom the Spartans hate. For this reason the Cretan War was unjust. “The Cretan War, if we wish to confess the truth,” says Florus, Book III, chapter 7, “we made from the desire merely to conquer a noble island. It seemed to have favored Mithridates; it pleased us to avenge this by arms, and, because the act was unjust, savage counsel was taken against the captives, so that very many destroyed themselves with poison.”
The second requirement is that they were not subjects of the enemies and that the cause of the war was not clear to them. For if the cause of war was doubtful, they were bound by treaty to furnish allies, arms, and provisions; since they must be judged innocent, they ought not to be harassed after the war is ended.
§ 10. It is not only a most just but also a most honorable cause of waging war when allies are defended. Thus the Roman people, moved by the prayers of Campania, attacked the Samnites, not on its own behalf but, what is more honorable, on behalf of its allies. In this matter it must also be observed that the cause of the allies be just.
Saint Chrysostom speaks beautifully on Psalm 134: “We have right hands from God so that we may bear aid both to ourselves and to others who have suffered injury, so that we may remove crimes from our midst, and so that we may be a harbor and refuge to those upon whom violence and injury are brought. How, then, shall pardon be given to those who use these arms not for salvation but for the destruction of others?” And this is what Cicero advises in Book IV of The Republic: “No war is undertaken by the best state except for safety or good faith.” For good faith must be kept with allies, lest they be allowed to be oppressed.
In this matter one must take care not to defend the unjust causes of allies. Some soldiers, for example, are so wicked that they care nothing whether the cause being conducted is just or evil. Having bound themselves for money, they serve the very powers of hell. A prince will not lightly employ them, because if money is displayed on the other side, they will soon migrate as deserters into the enemy’s camp. For this is in their mind:
Right is where the greatest reward is.
§ 11. Although soldiers and princes do not weigh matters in this way according to their proper importance, justice nevertheless requires that in an unjust war the commander and the soldiers make good the losses. In a doubtful case, ordinarily the prince must do so, because he ought to have investigated the matter more accurately, if he doubted through his own fault. Next, the counselors must do so, whose ignorance is inexcusable. Soldiers are bound to restore only that by which they have become richer. If the error of any soldiers was culpable, they are bound to return everything they took away. But through the calamities of war men are generally rendered worse. For they rage against the enemy, and once despoiled they turn to plunder; therefore the cause must be both just and weighty.