International Law

Body of law that governs relations between states and international organizations. Globalization—the phenomenon of growing worldwide economic, political, and social interconnectedness—has produced a need for internationally accepted norms to regulate the enormous amount of interaction across national boundaries. International law is an evolving body of treaties, conventions, customs, ideas, and protocols that govern state and nonstate behavior in international affairs.

There are two types of international law: public and private. Public law governs the relations between states or other entities, whereas private law governs specific, private transactions. These two types of law have been merging over time, forming the ever-growing institution of international law.

History and Origins

International law is generally recognized as having evolved over time, but most historians believe the Peace of Westphalia initiated the development of a formal body of international law. The end of the Thirty Years' War in 1648 saw the Western European powers free themselves from the political influence of the pope and the Holy Roman emperor. Before the war, European politics was dictated by the rivalry between pope and emperor. The kingdoms of Europe regularly lined up behind one or the other of these two powerful figures, who fought a seemingly endless series of wars for political dominance. After the Thirty Years&War, European states were free for the first time to set their own foreign policies. However, they lacked the security of the established order imposed by the papal-imperial relationship.

In the absence of an accepted set of rules for international conduct, European states sought a way to create a new political order that would establish norms of conduct and just action. The treaty known as the Peace of Westphalia, signed at the conclusion of the Thirty Years' War in 1648, was the first written statement of accepted conduct between sovereign nations. The treaty established moral, but secular, agree-ments—laws that were to be acceptable to all states, regardless of religion. This was a serious consideration in Europe, where Catholics and Protestants had fought for more than 100 years.

Sources of International Law

The Peace of Westphalia and subsequent agreements built on a long history of ideas of justice and right action. Divine law (morals universally ordained by a deity) and principles of natural law (the idea that humans, by virtue of their humanity, have certain rights and obligations) were two schools of thought that influenced thinking about international relations. Greek, Roman, Jewish, and Christian thought and scholarship also contributed to the theoretical basis of international law.

The work of the 16th-and 17th-century Dutch thinker Hugo Grotius is particularly important. His 1625 work De Jure Belli et Pacis (On the Law of War and Peace) laid out ideas about international relations that both religious and secular states could accept. His ideas were pragmatic and practicable, treading a middle path between blunt realism and lofty idealism. Grotius is often called “the father of international law.”

Historically, international law has drawn from religious and secular philosophical thought and existing custom. Contemporary international law expands on this existing base by incorporating modern writings and approaches. Common law (law based on tradition and precedent) is an important basis of international law and of states' understandings of appropriate behavior. The World Court, for example, recognizes written treaties, international custom (usual practice), general principles of law recognized by societies, and the judicial decisions of nations as valid sources of precedent for contemporary international law. Other possible sources include scholarly writings and UN resolutions. Of these, customs (customary law) and treaties are recognized as the strongest sources of international law; they tend to be acknowledged by most states on most occasions.

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