Modern international law began to develop with the rise of national states in Europe after the 15th century, when the basic ideas of national territory and jurisdiction were established. In 1625, building on the work of previous legal writers, the Dutch jurist Hugo Grotius published his celebrated treatise De Jure Belli ac Pacis (On the Law of War and Peace). Grotius argued that existing customs governing the relations between nations had the force of law and were binding unless contrary to natural justice or the law of nature (natural law), an immutable higher law governing all human conduct. Grotiuss influence on international affairs and the settlement of wars was great, and he is sometimes called the father of modern international law. His ideas became the cornerstone of the international system as established by the Peace of Westphalia (1648), a treaty that ended the Thirty Years War.

Other scholars and statesmen further described and developed the basic rules of international ...more