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War, in its juridical sense, is a contention carried on by force of arms between sovereign states, or communities having in this regard the right of states. The term is often used for civil strife, sedition, rebellion properly so called, or even for the undertaking of a State to put down by force organized bodies of outlaws, and in fact there is no other proper word for the struggle as such; but as these are not juridically in the same class with contentions of force between sovereign states, the jurist may not so use the term.

However, a people in revolution, in the rare instance of an effort to re-establish civil government which has practically vanished from the community except in name, or to vitalize constitutional rights reserved specifically or residuarily to the people, is conceded to be in like juridical case with a State, as far as protecting its fundamental rights by force of arms. Grote insisted that war was a more or less continuous condition of conflict between those contending by force; and so indeed it is; but even Grote, when seeking to determine the grounds of right and wrong in such a condition, necessarily moved the question back to the right to acts of force in either contending party, and so justified the more accepted juridical definition of a contest at arms between contending states. The judicial condition of the contending parties to the war is spoken of as a state of belligerency, while the term war more properly applies to the series of hostile acts of force exercised in the contention. To present here the position of Catholic philosophy in this regard, it will be convenient to discuss in sequence:

I. The Existence of the Right of War;
II. Its Juridical Source;
III. Its Possessor;
IV. Its Title and Purpose;
V. Its Subject-matter;
VI. Its Term.

From these we may gather the idea of a just war.


The right of war is the right of a sovereign state to wage a contention at arms against another, and is in its analysis an instance of the general moral power of coercion, i.e. to make use of physical force to conserve its rights inviolable. Every perfect right, i.e. every right involving in others an obligation in justice a deference thereto, to be efficacious, and consequently a real and not an illusory power, carries with it at the last appeal the subsidiary right of coercion. A perfect right, then, implies the right of physical force to defend itself against infringement, to recover the subject-matter of right unjustly withheld or to exact its equivalent, and to inflict damage in the exercise of this coercion wherever, as is almost universally the case, coercion cannot be exercised effectively without such damage. The limitations of this coercive right are: that its exercise be necessary ; and that damage be not inflicted beyond measure -- first of necessity and secondly of proportion with the subject-matter of right at issue. Furthermore, the exercise of coercion is restricted in civil communities to the public authority, for the reason that such restriction is a necessity of the common weal. In like manner the use of force beyond the region of defence and reparation, namely for the imposition of punishment to restore the balance of retributive justice by compensation for the mere violation of law and justice, as well as to assure the future security of the same, is reserved to public authority, for the reason that the State is the natural guardian of law and order, and to permit the individual, even in a matter of personal offence, to be witness, judge, and executioner all at once -- human nature being what it is -- would be a source of injustice rather than of equitable readjustment.

Now the State has corporate rights of its own which are perfect; it has also the duty to defend its citizens' rights ; it consequently has the right of coercion in safeguarding its own and its citizens' rights in case of menace or violation from abroad as well as from at home, not only against foreign individuals, but also against foreign states. Otherwise the duty above indicated would be impossible of fulfillment; the corporate rights of the State would be nugatory, while the individual rights of citizens would be at the mercy of the outside world. The pressure of such coercion, it is true, may be applied in certain circumstances without both parties going to the extreme of complete national conflict; but when the latter arises, as it commonly will, we have war pure and simple, even as the first application of force is initial warfare. Catholic philosophy, therefore, concedes to the State the full natural right of war, whether defensive, as in case of another's attack in force upon it; offensive (more properly, coercive), where it finds it necessary to take the initiative in the application of force; or punitive, in the infliction of punishment for evil done against itself or, in some determined cases, against others. International law views the punitive right of war with suspicion; but, thought it is open to wide abuse, its original existence under the natural law cannot well be disputed.


The source of the right of war is the natural law which confers upon states, as upon individuals, the moral powers or rights which are the necessary means to the essential purpose set by the natural law for the individual and the State to accomplish. Just as it is the natural law which, with a view to the natural purposes of mankind's creation, has granted its substantial rights to the state, so it is the same law which concedes the subsidiary right of physical coercion in their maintenance, without which none of its rights would be efficacious. The full truth, however, takes into consideration the limitations and extensions of the war-right set by international law in virtue of contract (either implicit in accepted custom or explicit in formal compact) among the nations which are party to international legal obligation. But it must be noted that civilized nations, in their effort to ameliorate the cruel conditions of warfare, have sometimes consented to allow, as the less of two imminent evils, that which is forbidden by the natural law. This is not strictly a right, though it is often so denominated, but an international toleration of a natural wrong. In the common territorial or commercial ambitions of great powers there may be an agreement of mutual toleration of what is pure and simple moral wrong by virtue of the natural law, and that without the excuse of it being a less evil than another to be avoided; in this case the unrighteousness is still more evident, for the toleration itself is wrong. The original determination of the right of war comes from the law of nature only; consent of mankind may manifest the existence of a phase of this law ; it does not constitute it.

The agreement of nations may surrender in common a part of the full right and so qualify it; or it may tolerate a limited abuse of it; but such agreement does not confer a particle of the original right itself, nor can it take aught of it away, except by the consent of the nations so deprived. The usage of the better part of the world in such a matter may be argued to bind all nations, but the argument does not conclude convincingly. The decisions of American courts lean toward the proposition of universal obligation : English jurists are not so clearly or generally in its favour. Of course, for that part of the international law bearing on war, which may be justly said to be the natural law as binding nations in their dealings with one another, the existence of which is manifested by the common consent of mankind, there can be no controversy: here the international law is but a name for a part of the natural law. Francisco Suárez, it is true, is inclined to seek the right of war as a means not precisely of defence, but of reparation of right and of punishment of violation, from the international law, on the ground that it is not necessary in the nature of things that the power of such rehabilitation and punishment should rest with the aggrieved state (though it should be somewhere on earth), but that mankind has agreed to the individual state method rather than by formation of an international tribunal with adequate police powers. However, the argument given above shows with fair clearness that the power belongs to the aggrieved state, and that though it might have entrusted, or may yet entrust, its exercise to an international arbiter, it is not bound so to do, nor has it done so in the past save in some exceptional cases.


The right of war lies solely with the sovereign authority of the State. As it flows from the efficacious character of other rights in peril, the coercive right must belong to the possessor, or to the natural guardian, of those rights. The rights in question may be directly corporate rights of the State, or which, of course, the State is itself the possessor, and of which there is no natural guardian but the sovereign authority of the State; or directly the rights of subordinate parts of the State or even of its individual citizens, and of these the sovereign authority is the natural guardian against foreign aggression. The sovereign authority is the guardian, because there is no higher power on earth to which appeal may be made; and, moreover, in the case of the individual citizen, the protection of his rights against foreign aggression will ordinarily become indirectly a matter of the good of the Commonwealth. It is clear that the right of war cannot become a prerogative of any subordinate power in the state, or of a section, a city, or an individual, for the several reasons: that none such can have the right to imperil the good of all the state (as happens in war) except the juridical guardian of the common good of all: that subordinate parts of the state, as well as the individual citizen, having the supreme authority of the state to which to make appeal, are not in the case of necessity required for the exercise of coercion; finally, that any such right in hands other than those of the sovereign power would upset the pace and order of the whole state. How sovereign authority in matter of war reverts back to the people as a whole in certain circumstances belongs for explanation to the question of revolution. With the supreme power lies also the judicial authority to determine when war is necessary, and what is the necessary and proportionate measure of damage it may therein inflict: there is no other natural tribunal to which recourse may be had, and without this judicial faculty the right of war would be vain.


The primary title of a state to go to war is:

  • first, the fact that the state's right (either directly or indirectly through those of its citizens) are menaced by foreign aggression not otherwise to be prevented than by war;
  • secondly, the fact of actual violation of right not otherwise reparable;
  • thirdly, the need of punishing the threatening or infringing power for the security of the future.

From the nature of the proved right these three facts are necessarily just titles, and the state, whose rights are in jeopardy, is itself the judge thereof. Secondary titles may come to a state,

  • first, from the request of another state in peril (or of a people who happen themselves to be in possession of the right );
  • secondly, from the fact of the oppression of the innocent, whose unjust suffering is proportionate to the gravity of war and whom it is impossible to rescue in any other way; in this latter case the innocent have the right to resist, charity calls for assistance, and the intervening state may justly assume the communication of the right of the innocent to exercise extreme coercion in their behalf.

Whether a state may find title to interfere for punishment after the destruction of the innocent who were in no wise its own subjects, is not so clear, unless such punishment be a reasonable necessity for the future security of its own citizens and their rights. It has been argued that the extension of a state's punitive right outside of the field of its own subjects would seem to be a necessity of natural conditions ; for the right must be somewhere, if we are to have law and order on the earth, and there is no place to put it except in the hands of the state that is willing to undertake the punishment. Still, the matter is not as clear as the right to interfere in defence of the innocent.

The common good of the nation is a restricting condition upon the exercise of its right to go to war; but it is not itself a sufficient title for such exercise. Thus the mere expansion of trade, the acquisition of new territory, however beneficial or necessary for a developing state, gives no natural title to wage war upon another state to force that trade upon her, or to extort a measure of her surplus territory, as the common good of one state has no greater right than the common good or another, and each is the judge and guardian of its own. Much less may a just title be found in the mere need of exercising a standing martial force, of reconciling a people to the tax for its maintenance, or to escape revolutionary trouble at home. Here, also, it is to be noted that nations cannot draw a parallel from Old-Testament titles. The Israelites lived under a theocracy ; God, as Supreme Lord of all the earth, in specific instances, by the exercise of His supreme dominion, transferred the ownership of alien lands to the Israelites ; by His command they waged war to obtain possession of it, and their title to war was the ownership (thus given them) of the land for which they fought. The privation thus wrought upon its prior owners and actual possessors had, moreover, the character of punishment visited upon them by God's order for offenses committed against Him. No state can find such title existing for itself under the natural law.

Furthermore, a clear title is limited to the condition that war is necessary as a last appeal. Hence, if there is reasonable ground to think that the offending state will withdraw its menace, repair the injury done, and pay a penalty sufficient to satisfy retributive justice and give a fair guarantee of the future security of juridical order between the two states concerned -- all in consequence of proper representation, judicious diplomacy, patient urgency, a mere threat of war, or any other just means this side of actual war -- then war itself cannot as yet be said to be a necessity, and so, in such premises, lacks full title. A fair opportunity of adjustment must be given, or a reasonable assurance had that the offence will not be rectified except under stress of war, before the title is just. Whether the aggrieved state should consent to arbitrate differences of judgment before resorting to war, is within its own competency to decide, as the natural law has established no judge but the aggrieved state itself, and international law does not constrain it to transfer its judicial right to any other tribunal, except in so far forth as it has by prior agreement bound itself so to do. None the less, when the grievance is not clear, and the public authority has sound reason to think that it can arrange for a tribunal where justice will be done, it would seem that the necessity of war in that individual case is not final, and even though international law may leave the state free to refuse all arbitration, the natural law would seem to commend if not to command it. Towards this solution of international differences, in spite of the difficulty of securing an unbiased tribunal, we have in the last fifty years made some progress.

Again, the question of proportion between the damages to be inflicted by war and the value of the national right menaced or violated must enter into consideration for the determination of the full justice of a title. Here we must take into account the consequences of such right being left unvindicated. Nations are prone to go to war for almost any violation of right, and its reparation absolutely refused. This tendency argues the common conviction that such violation will go from bad to worse, and that, if sovereign right is not recognized in a small thing, it will be far less so in a great. The conviction is not without rational ground; and yet the pride of power and the sensitiveness of national vanity can readily lead, in the excitement of the moment, to a mistaken judgment of a gravity of offence proportionate to all the ills of war. Neither is force a successful means of securing honour, unless it be to assure the due recognition of the rights of the sovereign power behind that honour ; while in the calm forum of deliberate reason the loss of one human life outweighs the mere offended vanity of a king or a people. The true proportion between the damage to be inflicted and the right violated is to be measured by whether the loss of right in itself or in its ordinary natural consequences would be morally as great a detriment to the common good of the state aggrieved as the damages which war conducted against the aggressor would entail upon the common good of the same, throwing into the balance against the latter the additional amount of damage due him as the punishment of retributive justice. Finally, a state going to war must weigh its own probable losses in blood and treasure, and its prospect of victory, before it may rightly enter upon a war: for the interest of the common good at home inhibit the exercise of force abroad, unless reasonably calculated not to be an ultimate graver loss to one's own community. This is not properly a limitation of title, but a prudential limitation upon the exercise of a right in the face of full title. The proper purpose of war is indicated by the title, and war conducted for a purpose beyond that contained in a just title is a moral wrong.


This will cover what may be done by the warring power in exercise of its right. It embraces the infliction of all manner of damage to property and life of the other state and its contending subjects, up to the measure requisite to enforce submission, implying the acceptance of a final readjustment and proportionate penalty; it includes in general all acts that are necessary means to such damage, but is checked by the proviso that neither the damage inflicted nor the means taken involve actions that are intrinsically immoral. In the prosecution of the war the killing or injuring of non-combatants (women, children, the aged and feeble, or even those capable of bearing arms but as a matter of fact not in any way participating in the war) is consequently barred, except where their simultaneous destruction is an unavoidable accident attending the attack upon the contending force. The wanton destruction of the property of such non-combatants, where it does not or will not minister maintenance or help to the state or its army, is likewise devoid of the requisite condition of necessity. In fact the wanton destruction of the property of the state or of combatants -- i.e. where such destruction cannot make for their submission, reparation, or proportionate punishment -- is beyond the pale of the just subject-matter of war. The burning of the Capitol and White House at Washington in 1814, and the devastation of Georgia, South Carolina, and the Valley of the Shenandoah during the American Civil War have not escaped criticism in this category. That "war is hell", in the sense that it inevitably carries with it a maximum of human miseries, is true ; in the sense that it justifies anything that makes for the suffering and punishment of a people at war, it cannot be ethically maintained. The defence, that it hastens the close of war through sympathy with the increased suffering even of non-combatants, will not stand. The killing of the wounded or prisoners, who thereby have ceased to be combatants, and have rendered submission, is not only no necessity, but beyond the limits of right because of submission, while common charity requires that they be properly cared for.

A doubt might arise about the obligation to spare wounded and prisoners, the guardianship or care of whom would prevent immediate further prosecution of the war at perhaps its most auspicious moment, or their dismissal but replenish the forces of the enemy. The care of the wounded might be waived, as its obligation is not of justice but of charity, which yields to a superior claim of one's own benefit: but the killing of prisoners presents a different problem. All practical doubt in the matter has been removed among civilized nations by the agreements of international law. The canons of the natural law of necessity and proportion this side the limit of intrinsic moral wrong are so hard of application by the contending forces that the history of wars is full of excesses; hence international law has steadily moved towards hard and fast lines that will lessen the waste of human life and the miseries of warfare. Thus the use of ammunition causing excessive destruction of human life or excessive suffering, incurable wounds, or human defacement beyond the requirements for putting the combatants out of the conflict and so winning a battle are excluded by international agreement based upon the obvious limitation of the natural law. Poisoning, as imperilling the innocent beyond measure, and assassination, as associated with treachery and the personal assumption of the right of life and death (to say nothing of its want of a fair opportunity of defence and the cowardice commonly implied therein), have met with common condemnation, thus closing the loophole of obscurity in the natural law. The natural law is clear enough, however, in condemning as intrinsically immoral lying and the direct deception of another, as well as bad faith and treachery. The phrase, "All is fair in love and war", cannot be taken seriously; it is a loose by-word taken from the reckless practices of men, and runs counter to right reason, natural law, and justice. No end justifies an immoral means, and lying, perjury, bad faith, treachery, as well as the direct slaughter of the innocent, wanton destruction, and the lawless pillage and outrage of cruder times, are, as far as the worst of them go, a thing of the past among civilized nations. That states are not always nice in conscience about lying, deceit, and bad faith in war as in diplomacy is occasionally a fact today; and the defence of lying and deceit in the stratagems of war, where good faith or common convention is not violated, is a sequence of the erroneous doctrine of Grote that lying is not intrinsically immoral, but only wrong in as far as those with whom we deal have a right to demand the truth of us; but as such teaching is almost unanimously repudiated in Catholic philosophy, the practice has today in Catholic thought no ethical advocate. The hanging of spies, though commonly said to be merely a measure of menace against a peculiar peril of war, would seem to have behind it a remote suggestion of punishment of a form of deceit which is intrinsically wrong.

In the terms of readjustment after victory, the victorious state, if its cause was just, may exact full reparation of the original injustice suffered, full compensation for all its own losses by reason of the war, proportionate penalty to secure the future not only against the conquered state, but, through fear of such penalty, even against other possibly hostile states. In the execution of such judgment the killing of surviving contestants or their enslavement, though, absolutely speaking, these might fall within the measure of just punishment, would today seem to be an extreme penalty, and the practice of civilization has abolished it.

Here we are confronted with the appalling destruction of the vanquished in the Old-Testament wars, where frequently all the adult males were slain after defeat and surrender, and sometimes even the women and children, unto utter extermination. But we cannot argue natural right from these instances, for, where justly done, this wholesale slaughter was the direct command of God, the Sovereign Arbiter of life and death, as well as the Just Judge of all reward and punishment. God by revelation made the Israelites but executioners of His supernatural sentence : the penalty was within God's right to assign, and within the Israelites' communicated right to enforce. The appropriation of a part of the territory of the vanquished may quite readily be a necessity of payment for reparation of injury and loss, and even the entire subjection of the conquered state, as a part of, or tributary to, its conqueror, may possibly fall within the proportionate requirements for full reparation or for future security, and, if so, such subjection is within the competency of the last adjudication. The history of nations, however, would indicate that this exaction was enforced far oftener than it was justified by proportionate necessity.


The term of the right of war is the nation against which war can justly be waged. It must be juridically in the wrong, i.e. it must have violated a perfect right of another state, or at least be involved in an attempt at such violation. Such a perfect right is one based upon strict justice between states, and so grounding an obligation in justice in the state against which war is to be waged. Here there is call for a distinction between the obligation of an ethical and a juridical duty. A juridical duty supposes a right in another which is violated by the state's neglect to fulfil that duty ; not so a merely ethical duty, for this is one proceeding from some other foundation than justice, and so implies no right in another which is violated by the non-fulfillment of the duty. The foundation of the right of war is a right violated or threatened, not a mere ethical duty neglected. No State, any more than an individual, may use violence to enforce its neighbour's performance of the latter. Hence a foreign state may have a duty to develop its resources not for its own immediate or particular need alone, but out of universal comity to help the prosperity of other states, for one community is bound to another by charity as are individuals ; but there is in another state no right to that development founded in justice. To assume that one state has the right to make war upon another to force it to develop its own resources is to assume that each state holds its possessions in trust for the human race at large, with a strict right to share in its usufruct inhering in each other state in particular -- an assumption that yet awaits proof. So, too, the need of one state of more territory for its overplus of population gives it no right to seize the superabundant and undeveloped territory of another. In the case of extreme necessity, parallel to that of a starving man, where there is not other remedy except forced sale or seizure of the territory in question, there would be something upon which to base an argument, and the case may be conceived, but seems far from arising. Similarly, a government's neglect of a juridical duty towards its own people of itself gives no natural right to a foreign state to interfere, save only in the emergency, extreme and rare enough, where the people would have the right of force against its government and by asking aid from abroad would communicate in part the exercise of this coercive right to the succouring power. Lastly, in the case of a state's wholesale persecution of the innocent with death or unjust enslavement, a foreign power taking up their cause may fairly be said reasonably to assume the call of these and to make use of their right of resistance.

In conclusion, a war, to be just, must be waged by a sovereign power for the security of a perfect right of its own (or of another justly invoking its protection) against foreign violation in a case where there is no other means available to secure or repair the right ; and must be conducted with a moderation which, in the continuance and settlement of the struggle, commits no act intrinsically immoral, nor exceeds in damage done, or in payment and in penalty exacted, the measure of necessity and of proportion to the value of the right involved, the cost of the war, and the guarantee of future security.

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