The legal process that concerns relations among nations is called international law. Belief and experience in some form of international law dates from at least the days of the Roman Empire. Such law differs greatly from national legal systems. No court has the authority or power to give judgments backed by coercive sanctions. Even in its most modern developments, international law is almost wholly based on custom. The precedents on which it rests are the acts of independent governments in their relations with one another, including treaties and conventions. Behind many of its rules is only a moral sanction: the public opinion of the civilized world. When treaties or conventions are involved, however, machinery to enforce them exists—either an arbitration or conciliation procedure or the submission of the dispute to a regional or international court.
A discernible body of rules and principles is observed or at least acknowledged in international relations. These rules concern such matters as territorial titles and boundaries, use of the high seas, limits on war, telecommunication, diplomatic and consular exchange, and use of air space. The major sources of international law on these matters are multilateral treaties, international custom, and such general principles as are recognized by civilized nations.
The United Nations is one of the primary mechanisms that articulate and create international law. The General Assembly and other agencies of the UN bring a combination of diplomacy, negotiation, and propaganda to bear on world affairs in ways that produce effective international treaties and affect world opinion. Certain courts also have indirect impact, including the International Court of Justice and the International War Crimes Tribunal. Domestic courts in various nations at times also engage in the articulation of international law.