Leiden Law Blog

Should Grotius still be considered the founding father of international law?

Should Grotius still be considered the founding father of international law?

Hugo Grotius (1583-1645) has long been synonymous with international law. Hamilton Vreeland’s Hugo Grotius: The Father of the Modern Science of International Law (1917) served to underline his status; the American Society of International Law holds an annual Grotius Lecture; and the Peace Palace library (The Hague) honors him as the “founder of the systematic modern doctrine of international law”. Modern international law includes inter alia the international criminal court, human rights, international treaties, and the United Nations. You might therefore expect its founding father to have been an advocate of at least some of these things—or at least, to provide a foundation for the principles that undergirds them. But is this the case?

His early work The Free Sea (1609) certainly contributes its eponymous doctrine to modern international law. Yet, a close reading of his mature and famous work The Law of War and Peace (1625) raises questions. In Book III, for instance, he writes that “killing is a right of war”, adding that it applies “to all persons who are in the enemy’s territory.” Also: “the right of killing such slaves [“captives taken in war”] is not restricted at any time”; and “included in the law of war” is “the slaughter even of infants and of women”. You may also devastate and pillage an enemy’s property. Prisoners may not only be killed or enslaved, but he also cites Seneca that: “There is no suffering which may not be inflicted upon such slaves, no action which may not be ordered, or forced by torture, to do, in any way whatsoever.” Ouch!

Morality and legality

Grotius is here offering a descriptive account of what he considers legitimate according to the law of nations—the broad, historically-grown international consensus. For Grotius, the law of nations may permit things in war that are forbidden by the law of nature—the moral laws derived from reason that apply where there are no human laws. And vice versa. He does urge his readers to refrain from killing, torture and destruction, and argues that, even in war, these brutal acts are often counterproductive and immoral.

Nevertheless, Grotius does describe them as both “permissible and “legitimate”. Curiously, the legal question and the moral question are separated. He did not write, “killing is an unfortunate result of war”, but “killing is the right of war”.  The only things truly forbidden—i.e. illegal—according to Grotius, are rape, poisoning weapons or wells, desecrating graves, or using assassins who would breach good faith in killing their target. For everything else: it may be immoral, but you do have the right.

This applies not only to the ius in bellum (book III) but also to the ius ad bello (book II). Both the Thomistic just war tradition and modern international law agree that there is a general moral judgment in the law against war unless certain conditions are met. For Grotius, the right to go to war—and private wars too!—is nearly a natural right, so long as one is preserving “life, limb” or “things useful to life”. Grotius argues that any war for the preservation of these and other rights is permissible; however, it may not be moral or prudent. By separating legal permissibility from moral justice, he seems to part company both with the ancient and the modern just war traditions. 


What also clearly sets Grotius apart from the modern understanding of international law, is that he is much more of a historical thinker—more a Roman than a Greek, as it were, and more medieval than modern. There is almost no talk of rights as they are conceived in the Universal Declaration of Human Rights. Rights, for Grotius, are either pre-political, perfect liberties (right to life), notably without duties attached, or they are historically-acquired privileges, such as contractual rights, or ownership of a slave. In a state of war, therefore, there are no natural, individual and human rights to consider. Actions and behavior in war are subject to moral considerations, but almost everything stands outside the spheres of legality and human rights.

An unfounded founding?

The question then is: To what extent can Grotius be considered the founder of modern International law, when almost everything we now consider as such—both the moral foundations and the institutional realities—he considers apart from, and outside of, law and legality? Grotius may justly be remembered as an advocate for moderation and good faith, especially in times of war; as well as discrete international law doctrines. But much of what now constitutes International law (e.g. crimes against humanity) were for Grotius parts of “moral justice” rather than legal justice. For him the idea of a world government or international court that could punish those responsible for atrocities accompanying war is very far afield. Sanctions against wrongs descended from virtue, the Gospels or historical precedent—the court of moral justice not that of legal justice.

The authors are currently preparing an academic paper on this topic.


Posted on June 4, 2015 at 10:24 by Sinead

The Italian Sir Alberico Gentili is the actual Father of international law. Others like are not.

Allen Guelzo
Posted on April 29, 2013 at 01:06 by Allen Guelzo

It was easier for Grotius to speak of tolerating “extreme” behavior in war when war more nearly resembled litigation between princes, and when monarchs possessed the exclusive right to the exercise of state violence. In the modern context of wars of entire nations and peoples against other nations and peoples, and with modern weapons, taking Grotius at face value can seem like an invitation to pure destruction.

Wouter Verheul
Posted on April 27, 2013 at 10:26 by Wouter Verheul

Surely the concept that there IS a law in times of war, is a requirement for what we today consider illegal wartime actions? Grotius may have been more “generous” with the limits on what one is allowed to do, but in order for our current understanding on illegal actions in war, first we need to accept that there ARE limitations (or can be).

Perhaps his emphasis on moral conduct also helped push us in that direction then? Moving away from sovereign powers who were used to doing whatever they considered necessary in war, towards an acceptance of limitations in wartime, based on morality. It’s hard to get a sovereign power to accept limitation to it’s conduct, after all…

So yes, a lot has changed since Grotius, but perhaps he IS the one who first set us on this road…what if he hadn’t written his works? Would our International Law regime be similar? I don’t know, but I’d love to hear your answers…

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