The Law of Nations or the Principles of Natural Law (1758)

Emmerich de Vattel

Of the Declaration of War: and of War in Due Form

§ 51. Declaration of war.
THE right of making war belongs to nations only as a remedy against injustice: it is the offspring of unhappy necessity. This remedy is so dreadful in its effects, so destructive to mankind, so grievous even to the party who has recourse to it, that unquestionably the law of nature allows of it only in the last extremity, — that is to say, when every other expedient proves ineffectual for the maintenance of justice. It is demonstrated in the foregoing chapter, that, in order to be justifiable in taking up arms it is necessary — 1. That we have a just cause of complaint. 2. That a reasonable satisfaction have been denied us. 3. The ruler of the nation, as we have observed, ought maturely to consider whether it be for the advantage of the state to prosecute his right by force of arms. But all this is not sufficient. As it is possible that the present fear of our arms may make an impression on the mind of our adversary, and induce him to do us justice, — we owe this further regard to humanity, and especially to the lives and peace of the subjects, to declare to that unjust nation, or its chief, that we are at length going to have recourse to the last remedy, and make use of open force, for the purpose of bringing him to reason. This is called declaring war. All this is included in the Roman manner of proceeding, regulated in their fecial law. They first sent the chief of the feciales, or heralds, called pater patratus, to demand satisfaction of the nation who had offended them; and if, within the space of thirty-three days, that nation did not return a satisfactory answer, the herald called the gods to be witnesses of the injustice, and came away, saying that the Romans would consider what measures they should adopt. The king, and in after times the consul, hereupon asked the senate’s opinion: and when war was resolved on, the herald was sent back to the frontier, where he declared it.2 It is surprising to find among the Romans such justice, such moderation and prudence, at a time too when, apparently, nothing but courage and ferocity was to be expected from them. By such scrupulous delicacy in the conduct of her wars, Rome laid a most solid foundation for her subsequent greatness.

§ 52. What it is to contain.
A declaration of war being necessary, as a further effort to terminate the difference without the effusion of blood, by making use of the principle of fear, in order to bring the enemy to more equitable sentiments, — it ought, at the same time that it announces our settled resolution of making war, to set forth the reasons which have induced us to take up arms. This is, at present, the constant practice among the powers of Europe.

§ 53. It is simple or conditional.
After a fruitless application for justice, a nation may proceed to a declaration of war, which is then pure and simple. But, to include the whole business in a single act, instead of two separate ones, the demand of justice (called by the Romans rerum repetitio) may, if we think proper, be accompanied by a conditional declaration of war, notifying that we will commence hostilities unless we obtain immediate satisfaction on such or such subject, in this case there is no necessity for adding a pure and simple declaration of war, — the conditional one sufficing, if the enemy delays giving satisfaction.

§ 54. The right to make war ceases on the offer of equitable conditions.
If the enemy, on either declaration of war, offers equitable conditions of peace, we are bound to refrain from hostilities: for as soon as justice is done to us, that immediately supersedes all right to employ force, which we are not allowed to use unless for the necessary maintenance of our rights. To these offers, however, are to be added securities; for we are under no obligation to suffer ourselves to be amused by empty proposals. The word of a sovereign is a sufficient security, as long as he has not disgraced his credit by any act of perfidy: and we should be contented with it. As to the conditions themselves, — besides the principal subject, we have a right to demand a reimbursement of the expenses incurred in our preparations for war.

§ 55. Formalities of a declaration of war.3
It is necessary that the declaration of war be known to the state against whom it is made. This is all which the natural law of nations requires. Nevertheless, if custom has introduced certain formalities in the business, those nations who, by adopting the custom, have given their tacit consent to such formalities, are under an obligation of observing them, as long as they have not set them aside by a public renunciation (Prelim. § 26). Formerly, the powers of Europe used to send heralds, or ambassadors to declare war; at present, they content themselves with publishing the declaration in the capital, in the principal towns, or on the frontiers: manifestoes are issued; and, through the easy and expeditious channels of communication which the establishment of posts now affords, the intelligence is soon spread on every side.

§ 56. Other reasons for the necessity of its publication.3
Besides the foregoing reasons, it is necessary for a nation to publish the declaration of war for the instruction and direction of her own subjects, in order to fix the date of the rights which belong to them from the moment of this declaration, and in relation to certain effects which the voluntary law of nations attributes to a war in form. Without such a public declaration of war, it would, in a treaty of peace, be too difficult to determine those acts which are to be considered as the effects of war, and those that each nation may set down as injuries of which she means to demand reparation. In the last treaty of Aix-la-Chapelle, between France and Spain on the one side, and England on the other, it was agreed that all the prizes taken before the declaration of war should be restored.

§ 57. Defensive war requires no declarations.
He who is attacked and only wages defensive war, needs not to make any hostile declaration, — the state of warfare being sufficiently ascertained by the enemy’s declaration, or open hostilities. In modern times, however, the sovereign who is attacked, seldom omits to declare war in his turn, whether from an idea of dignity, or for the direction of his subjects.

§ 58. When it may be omitted in an offensive war.
If the nation on whom we have determined to make war will not admit any minister or herald to declare it, — whatever the custom may otherwise be, we may content ourselves with publishing the declaration of hostilities within our own territories, or on the frontier; and if the declaration does not come to the knowledge of that nation before hostilities are commenced, she can only blame herself. The Turks imprison and maltreat even the ambassadors of those powers with whom they are determined to come to a rupture: it would be a perilous undertaking for a herald to go and declare war against them in their own country. Their savage disposition therefore, supersedes the necessity of sending one.

§ 59. It is not to be omitted by way of retaliation.
But no person being exempted from his duty for the sole reason that another has been wanting in his, we are not to omit declaring war against a nation, previous to commencement of hostilities, because that nation has, on a former occasion, attacked us without any declaration. That nation, in so doing, has violated the law of nature (§ 51); and her fault does not authorize us to commit a similar one.

§ 60. Time of the declaration.
The law of nations does not impose the obligation of declaring war, with a view to give the enemy time to prepare for an unjust defense. The declaration, therefore, need not be made till the army has reached the frontiers; it is even lawful to delay it till we have entered the enemy’s territories, and there possessed ourselves of an advantageous post: it must, however, necessarily precede the commission of any act of hostility, For thus we provide for our own safety, and equally attain the object of a declaration of war, which is, to give an unjust adversary the opportunity of seriously considering his past conduct, and avoiding the horrors of war, by doing justice. Such was the conduct of that generous prince, Henry the Fourth, towards Charles Emanuel duke of Savoy; who had wearied his patience by vain and fraudulent negotiations.4

§ 61. Duty of the inhabitants on a foreign army’s entering a country before a declaration of war.
If he, who enters a country with an army kept under strict discipline, declares to the inhabitants that he does not come as an enemy, that he will commit no violence, and will acquaint the sovereign with the cause of his coming, — the inhabitants are not to attack him; and should they dare to attempt it, he has a right to chastise them. But they are not to admit him into any strong-holds, nor can he demand admission. It is not the business of subjects to commence hostilities without orders from their sovereign: but if they are brave and loyal, they will, in the mean time, seize on all the advantageous posts, and defend themselves against any attempt made to dislodge them.

§ 62. Commencement of hostilities.
After a declaration of war on the part of the sovereign who has thus invaded the country, if equitable conditions are not offered him without delay, he may commence his operations; for, I repeat it, he is under no obligation to suffer himself to be amused. But, at the same time, we are never to lose sight of the principles before laid down (§§ 26 and 51) concerning the only legitimate causes of war. To march an army into a neighboring country by which we are not threatened, and without having endeavored to obtain, by reason and justice, an equitable reparation for the wrongs of which we complain, would be introducing a mode pregnant with evils to mankind, and sapping the foundations of the safety and tranquillity of states. If this mode of proceeding be not exploded and proscribed by the public indignation and the concurrence of every civilized people, it will become necessary to continue always in a military posture, and to keep ourselves constantly on our guard, no less in times of profound peace, than during the existence of declared and open war.

§ 63. Conduct to be observed towards the subjects of an enemy, who are in the country at the time of the declaration of war.5
The sovereign declaring war can neither detain the persons nor the property of those subjects of the enemy who are within his dominions at the time of the declaration. They came into his country under the public faith. By permitting them to enter and reside in his territories, he tacitly promised them full liberty and security for their return. He is therefore bound to allow them a reasonable time for withdrawing with their effects; and, if they stay beyond the term prescribed, he has a right to treat them as enemies, — as unarmed enemies, however. But, if they are detained by an insurmountable impediment, as by sickness, he must necessarily, and for the same reasons, grant them a sufficient extension of the time. At present, so far from being wanting in this duty, sovereigns carry their attention to humanity still farther, so that foreigners, who are subjects of the state against which war is declared, are very frequently allowed full time for the settlement of their affairs. This is observed in a particular manner with regard to merchants; and the case is moreover carefully provided for in commercial treaties. The king of England has done more than this. In his last declaration of war against France, he ordained that all French subjects who were in his dominions should be at liberty to remain, and be perfectly secure in their persons and effects, “provided they demeaned themselves properly,”

§ 64. Publication of the war, and manifestoes.
We have said (§ 56), that a sovereign is to make the declaration of war public within his dominions, for the information and direction of his subjects. He is also to make known his declaration of war to the neutral powers, in order to acquaint them with the justificatory reasons which authorize it, — the cause which obliges him to take up arms, — and to notify to them that such or such a nation is his enemy, that they may conduct themselves accordingly. We shall even see that this is necessary in order to obviate all difficulty, when we come to treat of the right to seize certain things which neutral persons are carrying to the enemy, and of what termed contraband, in time of war. This publication of the war may be called declaration, and that which is notified directly to the enemy, denunciation; and indeed the Latin term is denunciatio belli.

War is at present published and declared by manifestoes. These pieces never fail to contain the justificatory reasons, good or bad, on which the party grounds his right to take up arms. The least scrupulous sovereign would wish to be thought just, equitable, and a lover of peace: he is sensible that a contrary reputation might be detrimental to him. The manifestoe implying a declaration of war, or the declaration itself, printed, published, and circulated throughout the whole state, contains also the sovereign’s general orders to his subjects, relative to their conduct in the war.6

§ 65. Decorum and moderation to be observed in the manifestoes.
In so civilized an age, it may be unnecessary to observe, that, in those pieces which are published on the subject of war, it is proper to abstain from every opprobrious expression indicative of hatred, animosity, and rage, and only calculated to excite similar sentiments in the bosom of the enemy. A prince ought to preserve the most dignified decorum, both in his words and in his writings. He ought to respect himself in the person of his equals: and, though it is his misfortune to be at variance with a nation, shall he inflame the quarrel by offensive expressions, and thus deprive himself even of the hopes of a sincere reconciliation? Homer’s heroes call each other “dog” and “drunkard“: but this was perfectly in character, since, in their enmity, they knew no bounds. Frederic Barbarossa, and other emperors, and the popes their enemies, treated each other with as little delicacy. Let us congratulate our age on the superior gentleness of its manners, and not give the name of unmeaning politeness to those attentions which are productive of real and substantial effects.

§ 66. What is lawful war in due force.
Those formalities, of which the necessity is deducible from the principles and the very nature of war, are the characteristics of a lawful war in due form (justum bellum). Grotius says7 that, according to the law of nations, two things are requisite to constitute a solemn or formal war — first, that it be on both sides, made by the sovereign authority, — secondly, that it be accompanied by certain formalities. These formalities consist in the demand of a just satisfaction (rerum repetitio), and in the declaration of war, at least on the part of him who attacks: — for defensive war requires no declaration (§ 57), nor even, on urgent occasions an express order from the sovereign. In effect, these two conditions are necessarily required in every war which shall, according to the law of nations, be a legitimate one, that is to say, such a war as nations have a right to wage. The right of making war belongs only to the sovereign (§ 4); and it is only after satisfaction has been refused to him (§ 37), and even after he has made a declaration of war (§ 51), that he has a right to take up arms.8

A war in due form is also called a regular war, because certain rules, either prescribed by the law of nature, or adopted by custom, are observed in it.9

§ 67. It is to be distinguished from informal and unlawful war.
Legitimate and formal warfare must be carefully distinguished from those illegitimate and informal wars, or rather predatory expeditions, undertaken either without lawful authority or without apparent cause, as likewise without the usual formalities, and solely with a view to plunder. Grotius relates several instances of the latter.10 Such were the enterprises of the grandes compagnies which had assembled in France during the wars with the English, — armies of banditti, who ranged about Europe, purely for spoil and plunder: such were the cruises of the buccaneers, without commission, and in time of peace; and such in general are the depredations of pirates. To the same class belong almost all the expeditions of the Barbary corsairs: though authorized by a sovereign, they are undertaken without any apparent cause, and from no other motive than the lust of plunder. These two species of war, I say, — the lawful and the illegitimate, — are to be carefully distinguished, as the effects and the rights arising from each are very different.

§ 68. Grounds of this distinction.
In order fully to conceive the grounds of this distinction, it is necessary to recollect the nature and object of lawful war. It is only as the last remedy against obstinate injustice that the law of nature allows of war. Hence arise the rights which it gives, as we shall explain in the sequel: hence, likewise, the rules to be observed in it. Since it is equally possible that either of the parties may have right on his side, — and since, in consequence of the independence of nations, that point is not to be decided by others (§ 40), — the condition of the two enemies is the same, while the war lasts. Thus, when a nation, or a sovereign, has declared war against another sovereign on account of a difference arisen between them, their war is what among nations is called a lawful and formal war; and its effects are, by the voluntary law of nations, the same on both sides, independently of the justice of the cause, as we shall more fully show in the sequel.11 Nothing of this kind is the case in an informal and illegitimate war, which is more properly called depredation. Undertaken without any right, without even an apparent cause, it can be productive of no lawful effect, nor give any right to the author of it. A nation attacked by such sort of enemies is not under any obligation to observe towards them the rules prescribed in formal warfare. She may treat them as robbers,12 The inhabitants of Geneva, after defeating the famous attempt to take their city by escalade,13 caused all the prisoners whom they took from the Savoyards on that occasion to be hanged up as robbers, who had come to attack them without cause and without a declaration of war. Nor were the Genevese censured for this proceeding, which would have been detested in a formal war.


     1.    See in general, Grotius, B. iii. c. iv. s. 8: and 1 Chitty’s Com. Law, 378. — C.
     2.    Livy, lib. i. cap. 31.
     3.    But there seems to be no absolute necessity for a formal declaration of war to render it legal. See observations of Sir William Scott, in Nayede, 4 Rob. Rep. 252; Chitty’s Law Nat. 29, 3. But in England the king must have assented to a war to render it strictly legal. Brooke’s Abrid. tit. “Denizen,” pl. 26; The Hoop, 1 Rob. Rep, 196. — C. {The late war between the United States and Great Britain was declared by Act of Congress, June 18th, 1812. (Laws U.S. 1812, p. 227.) But war had existed, in fact, from March 4th until May 13th, 1846, between Mexico and the United States, without any formal declaration. The act of Congress of 13th May, 1846, declares that, “by the act of the Republic of Mexico,” war existed between the countries. (Laws U. States, 1846, p. 14.)}
     4.    See Sully’s Memoirs.
     5.    See in general 1 Chitty’s Com. L. 414. — C.
     6.    It is remarked as a very singular circumstance, that Charles the Second, king of Great Britain, in his declaration of war against France, dated February 9, 1668, promised security to French subjects who should “demean themselves properly,” — and, moreover, his protection and favor to such of them as might choose to emigrate to his dominions.
     7.    De Jure Belli et Pacis, lib. i. cap. iii. § 4.
     8.    Ante, the notes to the same sections. — C.
     9.    It has been laid down, that whenever the king’s courts are open in a given country, it is time of peace in judgment of law; but, when by hostile measures such courts are shut up or interrupted, then it is said to he time of war. Earl Lancaster’s case. Hale’s Pleas Crown, Part I. c. 26, p. 344; Co. Litt. 249 b. cited, and other points as to what is war; Elphinstone v. Bedreechund, Knapp’s Rep. 316. But at present, when in courts of justice, whether of Common Law, Equity, Admiralty, or Prize Court, it becomes necessary to ascertain what is, or not, evidence of a war, or a peace or neutrality, the same is now usually determined by distinct acts of the state. Upon this question, the following cases are material: — Sir Wm. Grant (in case of Pelham Burke, 1 Edward’s Rep. Appendix D; 3 Camp. 62; Blackburne v. Thompson, 15 East, 90, S.P.) observed, that, in order to ascertain whether or not a war or state of amity or neutrality subsists, it always belongs to the Government of the country to determine in what relation any other country stands towards it; and that is a point upon which courts of justice cannot decide; (i.e. without evidence aliunde as to the declarations or resolutions of Government;) and the most potent evidence upon such a subject is the declaration of the state. And if the state recognizes any place as being or as not being in the relation of hostility to this country, that is obligatory on courts of justice. Per Lord Ellenborough, 3 Camp. 66; and see other instances and authorities, 1 Chitty’s Commercial Law, 393-4. — C. (See, also, The U. States v. Palmer, 3 Wheat. Rep. 634, 635.)
     10.    Lib. iii. cap, iv.
     11.    See chap. xii. of this book.
     12.    Pirates may be lawfully captured by the public or private armed ships of any nation, in peace or war; for they are hostes humani generie. The Mariana Flora, 11 Wheat. Rep, 1.
     13.    In the year 1602.