On the Law of War and Peace by Hugo Grotius

First published: 1625

Type of work: Treatise on International Law

Critical Evaluation:

ON THE LAW OF WAR AND PEACE (DE JURE BELLI AC PACIS), the first systematic treatise on international law, remains a great landmark in the history of modern civilization and one of the foundations of modern international law. Grotius had a three-fold reason for writing his great book. First, he was morally and philosophically concerned with the problem of war. He was not a utopian who hoped to outlaw war, which he thought a regrettable but natural thing, but a practical attorney and an erstwhile public official who hoped to regulate and mitigate the horrors of conflict. As he says in his “Prolegomena” to ON THE LAW OF WAR AND PEACE, “Throughout the Christian world I observed a lack of restraint in relation to war, such as even barbarous races should be ashamed of; I observed that men rush to arms for slight causes, or no cause at all, and that when arms have once been taken up there is no longer any respect for law, divine or human; it is as if, in accordance with a general decree, frenzy had openly been let loose for the committing of all crimes.” Grotius says that he is fully convinced “that there is a common law among nations, which is valid alike for war and in war.” He hoped that by codifying and commenting on this “common law among nations” he would be able to create a base on which war could be understood and regulated.

His second reason for writing the book was his academic pride and self-interest. Grotius was as much a scholar as he was an active and practical man of affairs. He was one of the last great humanists; that is, one of the last great classical scholars of the Renaissance variety. To a great extent his ON THE LAW OF WAR AND PEACE is a scholarly study of classical Greek and Roman literature, science, and history aimed at understanding the classical experience of war, its causes, its conduct, and its effects. In this study he hoped to demonstrate, by the use of copious classical and biblical precedents, that there was indeed a set of natural and right laws pertaining to war and its conduct. Furthermore, he was aware that other scholars had attempted to make the same kind of study, but that all had failed. To complete such a study would, if nothing else, “contribute somewhat to the philosophy of the law.”

Finally, Grotius was ambitious. He was a political prisoner during the time he wrote the work and he undoubtedly hoped that it would impress the world and lead to his being brought back to a position of power and responsibility.

While the title of the book would indicate that Grotius was concerned equally with war and peace, the parts of the book that have to do with peace are only grafted onto the whole. The practical, as opposed to the scholarly, genesis of the work was Grotius’ experience in legal conflicts having to do with the law of prize and war on the high seas. This experience developed from certain legal problems that arose when the Dutch East India Company began to make inroads on the Portuguese trade monopoly in the Far East and Southeast Asia during the first decades of the seventeenth century.

What Grotius set out to do was to construct a system of law that was not based on the old principle of authority and decree, the principle on which was based the Roman law that dominated most of European legal study and which was the foundation of the Canon Law of the Roman Catholic Church. Grotius sought to replace the principle of authority with the principle of natural law common to all men and nations. The rationale of his system runs somewhat as follows: Like Aristotle, Grotius saw man as a social animal by nature. Just as it is natural that man should form societies, it is natural that he should have laws, since society cannot exist without laws, legal rights, and a system of justice. While law is natural to man, it is a conscious product of his reason, has been developed under the control of reason, and can be developed even further than necessity has so far demanded, by the further exercise of reason.

So far, law has been strictly a matter of individual and self-sufficient states. The law of one state has had no effect on the laws of another. But just as individual men band together naturally into nations, and in so doing engage in a social contract to limit themselves by the natural (but reasonable) laws required by their nations, so individual nations band together in civilizations. That is, nations no more than individuals can live in isolation; they must associate, and in associating they must, as is true of individuals, give up some of their sovereignty. For this reason it is natural that a system of laws, manifest in custom, consent, and contract, should spring up between states. Thus we have the law of nations, which should be adhered to with the same firmness as the domestic laws of an individual nation are adhered to by its individual citizens.

Finally, both of the two great kinds of law, domestic and international, are founded on God’s law. Since God created man and his nature, and since it is man’s nature to organize societies, and since it is natural for societies to band together in larger societies of nations, it is natural (by God’s plan) that there should be international law, codified and conforming to reason, which is also a part of man’s nature as created by God. All this is a part of God’s unchanging scheme of creation, and it remains only for the scholar to examine creation and human experience, and with the help of his reason perceive the structure of the Almighty’s scheme of natural law.

Founded on these principles, ON THE LAW OF WAR AND PEACE is divided into three major sections or books. Book One is largely concerned with the definition of war, whether it is lawful, and the nature of various kinds of war. Book Two attempts to examine the causes of war. Book Three is concerned with what is lawful and permissible in war.

In Book One, beginning with the idea that war is a condition of contending by force, Grotius states that war is undertaken in order to secure peace. That is, conflict precedes war. When peaceful means fail to end the conflict, and the conflict thus continues, war is resorted to in order to end conflict and thus bring peace. The author goes on to argue that war is not contrary to the law of nature, nor is it contrary to the law of the Gospels when the soldier fights in defense of virtue and duty. Having established the legality of war, and thus the necessity of regulating it by use of reason, Grotius distinguishes between public, private, and mixed war. “A public war is that which is waged by him who has lawful authority to wage it; a private war, that which is waged by one who has not the lawful authority; and a mixed war is that which is on one side public, on the other side private.” Interestingly, in discussing the question of whether an inferior may legally wage war against a superior, Grotius states the principle that underpinned many prosecution arguments at the Nuremburg War Crimes Trials after World War II: “Among all good men one principle at any rate is established beyond controversy, that if the authorities issue any order that is contrary to the law of nature or to the commandments of God, the order should not be carried out.”

Book Two begins with a consideration of the causes of war. The first cause is the necessity to defend self and property. Next in significance is injury, particularly injury to things which belong to men in common. Other causes discussed are acquisition of things (with particular reference, as is natural for a Dutchman, to the sea and rivers); assumed abandonment of ownership and occupation; property rights; obligations which arise from ownership; promises and alliances; and the desire to inflict punishment. These matters and many others are discussed in great detail. Book Two concludes with discussions of unjust causes of war, among which are fear, the wish for advantage apart from necessity, and the desire for world empire. Grotius also gives warnings not to undertake war rashly and considers the problems of war undertaken on the behalf of others.

Book Three begins with a discussion of “General Rules from the Law of Nature Regarding what is Permissible in War; with a Consideration of Ruses and Falsehood.” Grotius in discussing what is permissible in war makes a distinction between what is sanctioned by the law of nature on the one hand, and by the law of nations on the other hand. His first rule, which is based on the law of nature, is that “in war things which are necessary to attain the end in view are permissible.” As usual, Grotius, a Christian humanist who is discussing a frightful subject, finds that “things which are necessary” do not include all things: virtue and honor must be maintained even in the midst of deception and killing. Grotius goes on to discuss the legalities of war which must be legally declared by the proper authorities. He also examines and verifies the right of killing enemies in war, the right of devastation and pillage, the right over prisoners of war, and the right over the conquered. The second half of Book Three is concerned with mitigating the “rights” discussed in the first half and with the problem of ending war, as well as with many other matters and details.