Hugo Grotius (10 April 1583 – 28 August 1645), also known as Huig de Groot, Hugo Grocio or Hugo de Groot, was a jurist in the Dutch Republic. With Francisco de Vitoria and Alberico Gentili he laid the foundations for international law, based on natural law. He was also a philosopher, theologian, Christian apologist, playwright, and poet. Grotius’s influence on international law is paramount, and is acknowledged by, for instance, the American Society of International Law, which since 1999 holds an annual series of Grotius Lectures.

De Jure Belli ac Pacis

Living in the times of the Eighty Years’ War between Spain and the Netherlands and the Thirty Years’ War between Catholic and Protestant European nations (Catholic France being in the otherwise Protestant camp), it is not surprising that Grotius was deeply concerned with matters of conflicts between nations and religions. His most lasting work, begun in prison and published during his exile in Paris, was a monumental effort to restrain such conflicts on the basis of a broad moral consensus. Grotius wrote:

Fully convinced…that there is a common law among nations, which is valid alike for war and in war, I have had many and weighty reasons for undertaking to write upon the subject. 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.

De jure belli ac pacis libri tres (On the Law of War and Peace: Three books) was first published in 1625, dedicated to Grotius’ current patron, Louis XIII. The treatise advances a system of principles of natural law, which are held to be binding on all people and nations regardless of local custom. The work is divided into three books:

  • Book I advances his conception of war and of natural justice, arguing that there are some circumstances in which war is justifiable.
  • Book II identifies three ‘just causes’ for war: self-defense, reparation of injury, and punishment; Grotius considers a wide variety of circumstances under which these rights of war attach and when they do not.
  • Book III takes up the question of what rules govern the conduct of war once it has begun; influentially, Grotius argued that all parties to war are bound by such rules, whether their cause is just or not.

The arguments of this work constitute a theory of Just War. Roughly, the second book takes up questions of jus ad bellum (justice in the resort to war) and the third, questions of jus in bello (justice in the conduct of war). The way that Grotius conceived of these matters had, together with Francisco de Vitoria’s De potestate civili, a profound influence on the tradition after him and on the later formulation of international law.