International law includes both the customary rules and usages to which states have given express or tacit assent and the provisions of ratified treaties and conventions. International law is directly and strongly influenced, although not made, by the writings of jurists and publicists, by instructions to diplomatic agents, by important conventions even when they are not ratified, and by arbitral awards. The decisions of the International Court of Justice and of certain national courts, such as prize courts, are considered by some theorists to be a part of international law. In many modern states, international law is by custom or statute regarded as part of national (or, as it is usually called, municipal) law. In addition, municipal courts will, if possible, interpret municipal law so as to give effect to international law.
Because there is no sovereign supernational body to enforce international law, some older theorists, including Thomas Hobbes, Samuel Pufendorf, and John Austin have denied that it is true law. Nevertheless, international law is recognized as law in practice, and the sanctions for failing to comply, although often less direct, are similar to those of municipal law; they include the force of public opinion, self-help, intervention by third-party states, the sanctions of international organizations such as the United Nations, and, in the last resort, war.
National states are fundamentally the entities with which international law is concerned, although in certain cases municipal law may impose international duties upon private persons, e.g, the obligation to desist from piracy. New rights and duties have been imposed on individuals within the framework of international law by the decisions in the war crimes trials as well as the treaty establishing the International Criminal Court (see war crimes), by the genocide convention, and by the Declaration of Human Rights (see Economic and Social Council).
See also international relations.