Christopher C. Joyner
International law is the body of customs, principles, and rules recognized as effectively binding legal obligations by sovereign states and other international actors. 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 lawmaking process of the international community. Resolutions of international organizations, the United Nations in particular, may also affect the growth of the so-called customary international law that is synonymous with general principles of international law. The present system of international legal rules is based on the premise of state sovereignty. It is within the discretion of each state 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 United Nations is free to ratify any convention adopted by that agency.
American history confirms that the functions of international law and U.S. foreign policy are inextricably intertwined. The rules of modern international law are in great part products of negotiations in which U.S. diplomats played important roles, and U.S. foreign policy is in great part dependent on the rules of international law for its operation. The willingness of the U.S. government to employ international law as an instrument of foreign policy arises from the historical experience that shapes the political attitudes of the American people. Its vast size and abundant natural resources allowed the United States to grow into an economic power that rivaled its European peers. The United States was permitted to develop internally, in large measure without external distractions. Throughout the first half of the twentieth century, save for the interruption of World War I, the United States remained mainly on the sidelines, contributing little to expanding or modernizing the rules of international inter-course. After World War II, however, the United States emerged as a global superpower. Coincident with this newfound responsibility, and with the onset of Cold War rivalry with the Soviet Union, the United States asserted greater prominence in shaping the direction of international law—a role that became more salient over time.
To appreciate how international legal rules function in the making and performance of U.S. foreign policy, it must be understood that both tangible and intangible factors impose constraints on policymakers. The essence of these constraints lies within the nature of the international system.
See also DOCTRINES; ENVIRONMENTAL DIPLOMACY; EXCEPTIONALISM; HUMAN RIGHTS; HUMANITARIAN INTERVENTION AND RELIEF; INTERNATIONALISM; INTERNATIONAL MONETARY FUND AND WORLD BANK; INTERNATIONAL ORGANIZATION; INTERVENTION AND NONINTERVENTION; ISOLATIONISM; THE NATIONAL INTEREST; REALISM AND IDEALISM.