On the Law of War and Peace

A long Latin treatise in three books, written by the Dutch jurist Hugo Grotius in exile in Paris during the Thirty Years' War and dedicated to Louis XIII. Appalled by wars fought without restraint, Grotius set out to show that there is law binding nations in war as in peace. The Prolegomena grounds that law in human sociability and right reason, and makes the famous claim that natural law would hold even if, impiously, one granted that God did not exist. Book I asks whether any war can be just and defines war, right and law. Book II, the longest, sets out just causes of war, chiefly defence, recovery of what is owed and punishment, and along the way treats property, contracts, oaths, treaties, embassies and the right of passage. Book III asks what is permitted once war has begun and urges moderations that go beyond the strict letter of the law, sparing the innocent and keeping faith with enemies.

It is a founding text of international law and of modern natural law theory, and its questions about just causes and limits in war remain live in debates about intervention and conduct in war.