Hugo Grotius, The Law of War and Peace (1625)

Hugo Grotius was a central figure in the development of political and legal theory, especially the law of nations. The theme of war and its effect was Grotius’s chief concern and inspiration in De Jure Belli ac Pacis (hereinafter The Law of War and Peace.) As Stephen Neff declares in his introduction to Grotius’ work, “Hugo Grotius’s The Law of War and Peace could be described as a stately circumnavigation of the juridical world.”[1]

Writing in the early 17th century, when much of Europe was in turmoil, Grotius sought to identify principles of law that might offer a peaceful basis for resolving and preventing wars. His three-volume book, first published in 1625 and dedicated to Grotius’ patron at the time, Louis XIII, is regarded as the foundation of modern international law.[2] In The Law of War and Peace, Grotius developed a system of principles of natural law, which are held to be binding on all people and nations regardless of local customs.

Hugo Grotius was born in Delft, Netherlands in 1583. At the time, the Dutch war of independence from Spain was taking place. Grotius’ father was a staunch Protestant who held various posts in the city government.[3] Hugo was a child prodigy matched by few in the historical record. Indeed, in the 1920s, he even received the posthumous honor of tying for second place in a retrospective assessment of the IQs of three hundred noted geniuses in world history.[4] At the age of eleven, he enrolled in the Law Faculty at the University of Leiden, although his actual studies were in the liberal arts. His first exposure to public service came in 1598, at age fifteen, when he formed part of a Dutch diplomatic mission to King Henry IV of France. The journey to France was important for Grotius’ future. He registered at the University of Orleans for doctorate in law and the year he spent there was the only period of formal law study in his life. Returning to the Netherlands, he had a precocious career in Dutch law, politics and intellectual life. He was arrested in 1618 in a politico-religious dispute. After fleeing from prison in 1621 he spent most of the rest of his career in Paris.

Grotius’ many works discuss issues of the most diverse nature, ranging from history to literature. However, the writings that have transcended his time relate to his legal thinking and his contributions to law. Around 1604, the Dutch East India Company[5] asked Grotius for a brief explanation why they should be able to trade with territories claimed by the Portuguese. Grotius made the case that everyone had the right to use an ocean, irrespective of whom explored it. The Dutch East India Company decided against releasing the brief, titled De Jure Praedae, and consequently it was never published in its entirety. One of its key sections soon acquired universal renown under the title of Mare Liberum (The Free Sea), originally published anonymously in 1609.

It is important to mention briefly some of the ideas on the freedom of international navigation and trade developed in Mare Liberum, [6] because many of these ideas will further be advanced by Grotius in The Law of War and Peace. At the heart of his account resides the right of a state to trade with another, and with this, a claim for the legitimate use of violence to defend this right. It is essential to note that Mare Liberum is set within the context of the Dutch wars of independence and Dutch attempts at commercial expansion against Portugal. Here, Grotius attempts to prove false Portuguese juridical claims over the sea. At the time, Portuguese claims rested on two legal grounds: Papal decree and a treaty with Spain.[7] Grotius initiates his work by setting out a fundamental rule of the law of nations. He declares that “it is lawful for any nation to go to any other and to trade with it.”[8]

To some extent, Grotius’s justification for this claim builds upon the natural law theory of his predecessor, Francisco de Vitoria.[9] Grotius cites Vitoria and an Old Testament source of authority as basis for the right to travel across the earth and the right to just war when this is denied.[10] However, Grotius’ position on free trade differs from that of Vitoria. Grotius reconciles particular aspects of sixteenth century scholastic and humanist theories of property, while developing an original position,[11] especially relying on the notion of self-preservation,[12] in which the right of property and the right to defend it by violence is attached. Moreover, in Mare Liberum, as David Armitage notes, Grotius moves towards what he will depict in his theory in The Law of War and Peace. First, the argument that the freedom of the seas derives not only from nature but also from custom, and therefore from consent (an anticipation of his later theory of property in The Law of War and Peace, Book II. 2. 2); and, second, that the right to trade or navigation is legitimate not by virtue of it being a norm of objective justice, but because it was a moral faculty over a thing (an anticipation of his theory of rights in The Law of War and Peace BookI. 1. 4).[13]

In Mare Liberum, Grotius also in a sense frees nature from its dependence on Divinity. Although the idea of God runs throughout Grotius’ work, God does not play a crucial role. Indeed, the concept of God is reduced merely to the figure of “Creator.” God, for Grotius, is essentially one who has inscribed his principles in nature and has completely left it to its own inertia and foundational rules. Grotius says that God intervenes in human affairs indirectly through two judges who he has rooted on earth, conscience and public opinion.”[14]

Grotius began working on The Law of War and Peace in 1623. He took the title from a phrase in Cicero’s Oratio pro Balbo.  He expanded on the ideas and structure he had developed in De Jure Praedae. He was able to work rapidly and finished the text in a year. The book appeared in Paris in June 1625. It immediately incited controversy, especially among Catholics, who were shocked because Grotius did not refer to Popes by their Roman Catholic titles. The book was placed on the Papal Index in March 1626, and Roman Catholics were forbidden to read it.[15]

In The Law of War and Peace, Grotius’ ambition can be found in its title. His aim is not to establish whether there can be rules that govern war and peace, but to define what those rules are. In doing so he creates a system of law that could offer rights to both belligerents in war. Previous scholars and jurists on the laws of war had argued that either each belligerent could have an equal right to make war on the other[16], or that there was only one just belligerent.[17] In The Law of War and Peace, Grotius takes the middle ground and advances an entirely new legal approach. He argues that, although sovereigns could not have bilateral rights, their subordinates could, so that belligerents in the field of battle could be both lawful and just. This is put forward as a custom of war, found in jus gentium. Thus, Grotius develops a theory which claims that states have implicitly agreed that, regardless of the objective justice of their claims, soldiers can be recognized as having mutual and legitimate rights against each other in war.[18]

Grotius’ work consists of an introduction and three books, totaling more than 900 pages in translation. The introduction or Prolegomena holds the highest interest for scholars, for it is here that Grotius articulates and defends the philosophical foundations of his thought. Book One defines the concept of war, argues for the legitimacy of war, and identifies who may legitimately wage war. Book Two deals with the causes of war and enumerates three just causes for war: self-defense, reparation of injury and punishment. Finally, Book Three is dedicated mainly to the rightful conduct of belligerents in war, and it is where Grotius effectively argues that all belligerents are bound by the rules that govern the conduct of war once it has begun, whether their cause is just or not.

Grotius’ conception of human nature, as defined in the Prolegomena, suggests that man is perfectible, but not perfect. According to Richard Tuck, Grotius holds the view that, “the natural society of men is one in which individuals pursue their own interests up to the point at which such a pursuit actually deprives another of something which they possess…”[19] Thus, it is at the beginning of The Law of War and Peace that Grotius refers to the existence of a natural appetite for society, which is visibly not one of bare self-interest. Rather, Grotius compares this to the natural, unselfish attitude of compassion and care demonstrated by animals for their young or towards others of their species. He contends that: “Now amongst things particular to man, is his desire for society, that is, a certain inclination to live with those of his own kind, not in any manner whatever, but peaceably, and in a community, regulated according to the best of his understanding; which disposition the Stoics termed oikeiosis. Therefore the saying, that every creature is led by nature to seek its own private advantage, expressed thus universally, must not be granted.” Later, the Swiss legal theorist Emer de Vattel would note that “man is by nature sociable: society is natural for him, even necessary, if he is to pass his life happily. This is why the judicious Grotius has taken this sociability of man for the foundation of natural law.”[20]

In Book One, Grotius begins by asking whether it is ever lawful to wage war. If the initial inquiry reveals the possibility of a lawful war, the issue becomes that of determining which circumstances exist to distinguish between lawful and unlawful warfare. He argues that war is not only compatible with but sometimes compelled by all three major kinds of law: natural law, the law of nations and divine law. Grotius, like Alberico Gentili and Francisco de Vitoria before him, argues that there are certain circumstances, supported by the natural precepts of the law, which enable a nation to wage a war. In support of his position, he presents a number of conceptual, historical and theological arguments. Indeed, Grotius states that “in the first principles of nature there is nothing opposed to war; rather, they all favor it. For as the end of war is the preservation of our limbs, and the retention or acquisition of things useful to life, it accords well with those first principles. And to use force, if necessary, for the purpose, is no way contrary to the first principles of nature, since all animals are endowed by nature with strength, in order to protect and defend themselves…”[21]

As a way to clarify what these distinctive circumstances are, Grotius proceeds to define what is, in his view, lawful. He refers back to the principles of natural law and from there he sets the parameters of lawfulness. Indeed, a very large portion of The Law of War and Peace, some 40 per cent, comprises an extended treatment of natural law. However, the discussion of natural law in the main body of The Law of War and Peace appears almost by stealth.

Going forward, Grotius develops a simple but broad formula: everything that is just is also lawful. However, Grotius does not define what lawful is. Instead he simply states that something is lawful when it is simply not unlawful, when something is not “unjust.” He then defines “unjust” as contrary to natural reason, that is, the opposite of the rational nature of society expressed by the self-preservation instinct. Grotius notes that: “As the law of war is the title we give to this treatise, our first inquiry, as I have already stated, is whether any war can be lawful, and, in the next place, what is lawful in war. Law here signifies nothing but what is just, and that more in a negative than in a positive sense; so that a lawful thing is what is not unjust. Now anything is unjust which is opposed to the nature of a rational society.”[22]

Far from believing that war is a circumstance outside the realm of morality and law, Grotius takes it to be an instrument of right.[23] Indeed, he says that “where judicial settlement fails, war begins.”[24] Since Grotius understands that the recourse to war is legally valid, in so far as it aims to punish, repair, amend or compensate injuries caused by an unjust act, it follows, then, that war is not banned by the natural law. Rather, natural law supports it, since unjust acts are ultimately transgressions of natural law provisions.

Some scholars have argued that what sets Grotius’ examination of jus ad bellum apart from his predecessors is “his detailed and systematic elaboration of the “just causes of war.”[25] Considering that any act contrary to natural law (any unjust act) may constitute a “casus belli,”[26] Grotius begins to extract from this abstract principle specific guidelines. He exposes in Book Two various reasons, in light of his own legal system, which would permit waging a “just war.” He contends that “God wills that should we protect ourselves, retain our hold on the necessities of life, obtain that which is our due, punish transgressors, and at the same time defend the state …Therefore, some wars are just.”[27] Wars may be justly undertaken in response either to “wrongs not yet committed, or to wrongs already done.”

It is important to note that Grotius omits to mention religion as a just cause of war. And this fact is not an accident. Indeed, in one chapter of The Law of War and Peace, which specifically focuses on the “illegal reasons for going to war,” Grotius makes explicit reference to the subject of religion and makes it clear that the message of Jesus was to reveal his word and extend his “kingdom” “not by coercion but by persuasion.”[28]

Because Grotius makes the violation of natural law as the core “casus belli,” he leaves the window open to endless possibilities for reparations. The scope of his proposal is wide-ranging. For example, a state not directly involved in any confrontation may embark on a bellum justum to restore natural law violated by another state. Whereas Grotius defends the right of non-intervention, and does not hesitate to affirm that an individual is always subject to the jurisdiction and the possibility of punishment by his state, he admits, however, that when that same state commits humanitarian violations, another state is allowed to intervene in defense of the victims. As Theodor Meron notes, although Grotius “… believed that, subject to some significant exceptions, even in the case of ‘extreme necessity’ subjects might not rebel against their ruler, Grotius still maintained the lawfulness of intervention by one state on behalf of gravely persecuted citizens of another. He was aware of the ever-present potential for abuse but insisted that occasional abuses did not render the right of intervention invalid.”[29] In this regard, Grotius considers that persecution, slaughter, and any general human humiliation, are not only crimes perpetrated against a particular man or a group of men, but are a violation of natural law and therefore an offense against all humanity.

Grotius’ humanist conception of the legal system reflects the influence of Gentili (who held a similar thesis[30]); but also mark Grotius as a forerunner of modern international law concepts (for example, recognizing the universal jurisdiction of war crimes and crimes against humanity).

Once war has begun, it must also be fought justly for it to be just. While Grotius outlines the general rule that “in war things which are necessary to attain the end in view are permissible,”[31] it should be noted that what Grotius means by “the end in view” is the restoration of natural law violated by a state or, what is the same for Grotius, the service to what is morally right. This general premise, quite vague conceptually, begins to be progressively restricted by Grotius as he defines what is for him “right.” For Grotius, if war cannot always be avoided, at least the killing and destruction must be limited. He believes that “it is folly, and worse than folly, wantonly to hurt another…War is a matter of gravest importance, because so many calamities usually follow in its train, even upon the head of the innocent. So, where counsels conflict we ought to incline toward peace…It is often a duty, which we owe to our country and ourselves, to forbear having recourse to arms… [the] conquered should be treated with clemency, in order that the interests of each may become the interests of both.”

In Book Three, Grotius considers the permissibility of a large number of actions. The range and amount of detail in this discussion is captivating. One distinctive feature is his analysis of ruses, deceit and falsehood, as he not only discriminates between those three means of conveying false impressions, but also distinguishes discrepancies within each of them.[32] The practical purpose of Book Three is evident. The priority for Grotius seems to be clarifying what exactly is and is not permitted in war. Thus, Grotius holds that war is justifiable when, and only when, it serves right. Since the conditions for service to right are numerous, he must devote significant effort identifying and illuminating them.[33]

Grotius contends that while an armed conflict is taking place the application of civil laws should be interrupted and, instead, certain rules should go into effect which, according to natural law, will moderate war. Thus, it is necessary, before the beginning of any confrontation, to explicitly declare war to the opponent. Moreover, for a war to be lawful it must be declared by a legitimate and sovereign authority. In this regard, Grotius says: “It is evident, that no war is considered to be lawful, regular and formal except that which is began and carried on by the sovereign power of each country.”[34] During war, Grotius argues, there exists a right to kill enemies, as long as these enemies are not women, children, prisoners, or other innocent civilians. He advocates the right to take prisoners but not to execute them.[35] He argues that “it had long being a maxim, universally received among the powers of Christendom, that prisoners of war cannot be slaves…” He recognizes the possibility of taking the enemy’s possessions for the purpose of financing the war, or as a means to compensate the damages inflicted by the other party to the conflict. He advises limiting what might be seized from an adversary, however. He states that “the law of nature indeed authorizes our making such acquisitions in a just war, as may be deemed an equivalent for a debt, which cannot otherwise be obtained, or as may inflict a loss upon the aggressor, provided it be within the bounds of reasonable punishment.”  In the same way, he insists that retaliation “must be directly enforced upon the person of the delinquent himself.” In addition, Grotius emphasizes that all actions performed during warfare and until its conclusion, should be proportional. For it is understood that the means used to remedy the injury caused, should never exceed what is necessary. Thus, the killing of hostages or prisoners is an action condemned by Grotius.

The Law of War and Peace covers all the main questions that are relevant for the laws of war, even in our present time. While all these questions had been raised earlier by various jurists and scholars, Grotius expanded them and proposed that the laws of war were supported by natural law. Using old sources, Grotius opened new possibilities of thinking and acting for his contemporaries that were not visible earlier, or at least not in the same way. And his fame and influenced eventually outshined that of Vitoria, Gentili and other earlier scholars who greatly contributed to Grotius’ ideas.

Hugo Grotius has been regarded by scholars not only as the father of international law but also as the source of the tradition of “international society” and “solidarism” for example.[36] In addition, The Law of War and Peace is considered the first general comprehensive modern work grounded on reason and natural law. Indeed, there is a long line of scholars who comfortably classify Grotius as the founder of the modern natural law tradition. As Michael Donclan notes, “his book is devoted to putting once again at unprecedented length the traditional case for saying that there is a law common to all men, the natural law … the deepest layer of Grotius’ thought … is the natural law.”[37] Grotius’ concept of natural law had a strong impact on the philosophical and theological debates and political developments of the 17th and 18th centuries. Among those he influenced were Samuel Pufendorf and John Locke, and via these thinkers Grotius’ ideas became part of the cultural background of the Glorious Revolution in England and the American Revolution.[38]

However, critics of Grotius compare his work with the work of his predecessors to dispute against Grotius’ originality. For example, W. Knight argues that The Law of War and Peace is really “no more than a restatement of principles which had already for generations been commonplaces of the schools, and particularly of the neo-scholastics of Spain.”[39] Similarly, Stephen Neffs argues that Grotius was not the Isaac Newton or the Galileo Galilei of international law, but that “his instincts were firmly in the past, in the rationalist tradition of natural law extended back to Aquinas.”[40] Other scholars, such as Peter Haggenmaker, argue that The Law of War and Peace cannot be seen as the precursor of the system of international law that developed subsequently, and that it is instead a much more scientifically rigid and limited work whose sole aim was to set out a general theory of the laws of war.[41]

As seen above, Grotius’ primary goal was to counter the two established philosophies of war and peace at the time, thus developing a new system in their place. He claimed that the alternative philosophies of war and peace were both excessive and absolute in the extent and limits they sought to place upon war. A secondary goal of his work was to introduce a concept of “moderation” into the practice of warfare. His call for the application of this virtue formed several chapter headings of Book Threeof The Law of War and Peace.

Grotius succeeded in developing, and insisting upon, the idea of justice among nations. With that purpose in mind, Grotius aimed to support the resolution of persistent international conflicts and to provide the legal and moral arguments for wars becoming less frequent and less atrocious. Indeed, Grotius advanced principles to help expand the prospects for peace. As historian John Neville Figgis noted, Hugo Grotius and his successors succeeded in placing some boundaries to the unlimited predominance of “reason of state.”[42]

Stephen Neff recalls in his book the anecdote of Swedish King Gustavus Adolphus carrying a copy of the 1625 edition of Hugo Grotius’s The Law of War and Peace with him on military campaigns. Between 1550 and 1815, Neff notes, the subtle movement toward abandoning the just war doctrines and accepting the practical result that, given the ambiguity of who was acting “justly,” both sides would be regarded as having equal rights to “exercise the normal prerogatives of just belligerents.”[43] This indeed is evidence of Grotius’ impact on state practice. The Law of War and Peace greatly influenced the norms and practices of international conduct.

Kingsbury and Roberts argue that the greatest direct contribution of The Law of War and Peace is “the systematic reassembling of practice and authorities on the traditional but fundamental subject of the jus belli, organized for the first time around a body of principles rooted in the law of nature.”[44] Grotius believed that only a rational approach to the realities of international politics could settle the serious conflicts that plagued the various nations in seventeenth-century Europe. Grotius ‘ work rested on the assumption that natural law was intrinsically simple and evident, that anyone who properly used reason could recognize and obey it. Grotius stated: “This maintenance of the social order…is the source of law properly so called…Since over other animals man has the advantage of possessing not only a strong bent toward social life, of which we have spoken, but also a power of discrimination which enables him to decide what things are agreeable or harmful.” [45] Once he defined the broad outlines of natural law, Grotius attempted to harmonize natural law and positive law. And by doing so, the Dutch jurist was able to develop a general normative framework, valid for all nations, a positive law of nations, the future modern international law.

 

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Keene, Edward. Beyond the Anarchical Society: Grotius, Colonialism and Order in World Politics, (Cambridge: Cambridge University Press, 2002).

Knud, Haakonsen. Natural Law and Moral Philosophy from Grotius to the Scottish Enlightenment, (Cambridge, Cambridge University Press, 1996).

Pagden, Anthony. ed., The Languages of Political Theory in Early-Modern Europe, (Cambridge University Press, 1987).

Padgen, Anthony. The Burden of Empires: 1539 to the Present (Cambridge University Press, 2015).

Tuck, Richard. The Rights of War and Peace: Political Thought and the International

Order From Grotius to Kant (Oxford: Oxford University Press, 1999).

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