principles and rules of conduct that nations regard as binding upon them and, therefore, are expected to and usually do observe in their relations with one another. International law is the law of the international community.

Ancient History.

The need for some principles and rules of conduct between independent states arises whenever such states enter into mutual relations. Rules governing the treatment of foreign traders, travelers, and ambassadors, as well as the conclusion and observance of treaties, developed early in human history. The oldest known treaty, preserved in an inscription on a stone monument, is a peace treaty between two Sumerian city-states, dating from about 3100 bc. A considerable number of treaties concluded by the empires of the ancient Middle East during the 2d millennium bc show rudimentary notions of international law. In later antiquity the Jews, Greeks, and Romans developed tenets of international law. Jewish law as set forth in the Book of Deuteronomy contains prescriptions for the mitigation of warfare, notably prohibitions against the killing of women and children. The Greek city-states created an elaborate treaty system governing a multitude of aspects of the relations among themselves. The conduct of the Olympic Games and the protection of religious sanctuaries, such as the Temple of Delphi, were among the subjects of some of these inter-Greek treaties.

Even more than other ancient people, the Romans made significant contributions to the evolution of international law. They developed the idea of a jus gentium, a body of laws designed to govern the treatment of aliens subject to Roman rule and the relations between Roman citizens and aliens. They were the first people to recognize in principle the duty of a nation to refrain from engaging in warfare without a just cause and to originate the idea of a just war.

The Modern System.

Modern international law emerged as the result of the acceptance of the idea of the sovereign state, and was stimulated by the interest in Roman law in the 16th century. Building largely on the work of previous legal writers, especially Spanish precursors, the Dutch jurist Hugo Grotius, sometimes called the father of modern international law, published his celebrated treatise De Jure Belli ac Pacis (On the Laws of War and Peace) in 1625. (Prior to that time he had published his pioneering tract on freedom of the sea, Mare Liberum, 1609.) Grotius based his system on the law of nature and propounded the view that the already existing customs governing the relation between nations had the force of law and were binding unless contrary to natural justice. His influence on the conduct of international affairs and the settlement of wars was great. His ideas became the cornerstone of the international system as established by the Peace Treaties of Westphalia (1648), which ended the Thirty Years’ War.

Other scholars and statesmen further developed the basic rules of international law, among them the Dutch jurist Cornelis van Bynkershoek (1673–1743) and the Swiss diplomat Emmerich de Vattel (1714–67) whose Le droit des gens (1758; Law of Nations) exercised great influence on the framers of the U.S. Constitution. By the end of the second half of the 19th century the literature on the subject had reached vast proportions. The Institute of International Law, a private organization for the study of international law composed of outstanding scholars from various countries, was established in 1873. One of its founders was the American David D. Field, who in the same year had authored Outlines of an International Code.

International law stems from three main sources: treaties and international conventions, customs and customary usage, and the generally accepted principles of law and equity. Judicial decisions rendered by international tribunals and domestic courts are important elements of the law-making process of the international community. UN resolutions now may also have a great impact on the growth of the so-called customary international law that is synonymous with general principles of international law.

The present system of international law is based on the sovereign state concept. It is within the discretion of each state, therefore, to participate in the negotiation of, or to sign or ratify, any international treaty. Likewise, each member state of an international agency such as the UN is free to ratify any convention adopted by that agency.

Treaties and conventions were, at first, restricted in their effects to those countries that ratified them. They are particular, not general, international law; yet regulations and procedures contained in treaties and conventions have often developed into general customary usage, that is, have come to be considered binding even on those states that did not sign and ratify them. Customs and customary usages otherwise become part of international law because of continued acceptance by the great majority of nations, even if they are not embodied in a written treaty instrument. “Generally accepted principles of law and justice” fall into the same category and are, in fact, often difficult to distinguish from customs.

Since the beginning of the 19th century, international conferences have played an important part in the development of the international system and the law. Noteworthy in that respect was the Congress of Vienna which, through its Final Act of 1815, reorganized Europe after the defeat of Napoleon and also contributed to the body of international law. For example, it established rules for diplomatic procedure and the treatment of diplomatic envoys. On the urging of Great Britain, it included a general condemnation of the slave trade. Another important step in the development of international law was the Conference of Paris (1856), which was convened to terminate the Crimean War but at the same time adopted the Declaration of Maritime Law that abolished privateering and letters of marque, modernized the rights of neutrals during maritime war, and required blockades to be effective. The Declaration of Paris also initiated the practice of providing for the subsequent accession by nations other than the original signatories. In 1864 a conference convened in Geneva at the invitation of the Swiss Federal Council approved a convention for the protection of wounded soldiers in a land war; many nations subsequently acceded to this convention.

The avoidance or mitigation of the rigors of war continued to be the subject of other multilateral treaties. The peace conferences held in 1899 and 1907 in The Hague, the Netherlands, resulted in a number of conventions of that type. The 1899 conference adopted a Convention for the Pacific Settlement of International Disputes, which created the Permanent Court of Arbitration. Although it was not a veritable court with a fixed bench of judges, it served as an important instrument of arbitration.

At the end of World War I the League of Nations was established by the covenant signed in 1919 as part of the Treaty of Versailles. Pursuant to provisions in this covenant, the Permanent Court of International Justice was established in 1921. The League of Nations was created as a permanent organization of independent states for the purpose of maintaining peace and preventing war. During its existence 63 countries were members of the League at one time or another. The USSR joined in 1934, but Germany and Japan withdrew in 1933. The U.S. never became a member of the organization, which was powerless to forestall World War II. Equally unsuccessful in preventing hostilities was the Pact of Paris for the Renunciation of War (1928)—the so-called Kellogg-Briand Pact—although it was ratified by more than 60 nations, including Germany and Japan. After the termination of World War II in 1945 the UN Charter created a new organization with an elaborate machinery for solving disputes among nations and for the further development of international law.

Normally, every nation is expected to obey international law. Some nations, for example Great Britain, have incorporated into their municipal law the provision that international law shall be made part of the law of the land. The U.S. Constitution empowers Congress “to define and punish . . . Offences against the Law of Nations.” (Article I, Section 8). In cases involving international law, American courts tend to interpret American law in conformity with international law; such an attitude has consistently been urged by the U.S. Supreme Court.

If each nation were free to declare unilaterally that it is no longer bound by international law, anarchy would result, as seen in the conduct of Germany under Nazi rule. The Nuremberg tribunals held that the German government regulations that ordered, for example, the killing of prisoners of war in contravention of the generally valid rules of warfare were null and void and that the persons who issued and executed such orders were criminally responsible for violations of international law (see WAR CRIMES TRIALS, ).

Impact of the UN on International Law.

The UN began its life with a membership of 50 nations. In the 1990s, because of the growth of newly independent nations, the number exceeded 180. The aims and purposes of the organization encompass the maintenance of peace and security and the suppression of acts of aggression. The Charter also expressly includes among its objectives the maintenance of respect for the obligations arising from treaties and other sources of international law. For that reason the Charter established the International Court of Justice as one of the most important UN organs and specifically charged the General Assembly with the progressive development and codification of international law. To carry out this task, the General Assembly has created two subsidiary organs: the International Law Commission and the Commission on International Trade Law. The International Law Commission, on assignment by the General Assembly, has prepared drafts of treaties codifying and modernizing a number of important subjects of international law, such as various aspects of the law of the sea (1958), diplomatic relations, consular relations, law of treaties between nations, succession of states in respect to treaties, law of treaties between nations and international organizations, and immunity of states from the jurisdiction of other states. Upon acceptance by the General Assembly, these drafts are submitted to international conferences convoked by the UN for the negotiation of the respective conventions.

In some instances, the UN has convoked conferences to negotiate treaties without prior proposal by the International Law Commission. The most important example was the third UN Conference on the Law of the Sea which terminated its work in 1982 with the draft of a convention for a comprehensive regime governing all aspects of the peaceful use of the oceans. Another example is the text of the convention governing the activities of nations on the moon and other celestial bodies, which was adopted by the General Assembly in 1979 and went into effect in 1984.

Since the UN Charter bans the use of force against the territorial integrity or political independence of any state, the UN has refrained from addressing aspects of the law of war and neutrality. Nevertheless, the four Geneva conventions of 1949—the so-called Red Cross Conventions—formulated improved agreements relative to the amelioration of the condition of wounded and sick members of the armed forces in the field and at sea, the treatment of prisoners of war, and the protection of civilian persons in wartime, thereby instilling new life into the humanitarian principles of international law.

International law regulates intercourse among nations in peacetime and provides methods for the settlement of disputes by means other than war. Apart from procedures made available by the UN, these methods include direct negotiation between disputants under the established rules of diplomacy, the rendering of good offices by a disinterested third party, and recourse to the International Court of Justice. Other peacetime aspects of international law involve the treatment of foreigners and of foreign investments; the acquisition and loss of citizenship; and status of stateless persons; the extradition of fugitives; and the privileges and duties of diplomatic personnel.

Human Rights.

Since World War II international law has become increasingly concerned with the protection of human rights. It has provided improved procedures for that purpose within the UN. This new emphasis has also been manifested in the adoption by the UN of the Universal Declaration of Human Rights and the conclusion of the Convention on the Prevention and Punishment of the Crime of Genocide in 1948, the signing of the International Convention on the Elimination of All Forms of Racial Discrimination in 1966, and the adoption in 1975 of the Declaration on the Protection of All Persons from Being Subjected to Torture or Other Cruel, Inhuman or Degrading Treatment or Punishment. These measures have been supplemented by regional conventions, such as the European Convention for the Protection of Human Rights and Fundamental Freedoms (1950) and the American Convention on Human Rights (1969). In 1945 an international convention for the prosecution of the major war criminals of the European Axis powers provided for the punishment of crimes against humanity and established a special International Military Tribunal for that purpose. At present, however, no international tribunal with jurisdiction over such crimes is in existence.

New threats constantly call for new international responses. Examples are the conventions against acts of terrorism and the distribution of drugs. Despite the modern multiplication of global and regional multilateral treaties, however, customary international law still maintains a central role in the legal system of the international community.        D.C., DAVID CARLINER, LL.B.S.A.R., STEFAN A. RIESENFELD, J.S.D., LL.B.

For further information on this topic, see the Bibliography, section 248. International law.