Grotius' On the Law of War and Peace

In 1625, while living in exile in Paris, the Dutch lawyer and scholar Hugo Grotius published De Jure Belli ac Pacis, On the Law of War and Peace. Its three books ask when a war is just, what is allowed in fighting it, and how peace should be kept. The book is widely seen as a founding text of international law, because it describes rules that bind states toward each other, not just subjects toward a ruler.¹²

Grotius wrote in the middle of the Thirty Years' War, which was killing a large share of the people of central Europe. He drew on Roman law, on Spanish scholars such as Francisco de Vitoria, and on classical writers, but he also had personal reasons. In 1604 to 1605 he had written a defense of the Dutch East India Company's capture of a Portuguese ship, and one chapter, published in 1609 as Mare Liberum, argued that the seas are open to all. Sentenced to life in prison in a Dutch religious and political struggle, he escaped Loevestein Castle in 1621, reportedly hidden in a chest of books.¹³

His central claim is that natural law, grounded in reason and human sociability, would bind rulers even if one set aside religion. Wars need a just cause, such as self-defense or redress of a wrong, and treaties must be kept. His ideas shaped the diplomats who ended the Thirty Years' War at Westphalia in 1648, and later thinkers such as Vattel, along with the 1899 Hague conferences and the UN Charter's rules on force. Critics, from Kant, who called such writers 'sorry comforters', to modern scholars, note that his rules often justified European colonial conquest.²³