U.S. foreign relations depend on legal order, operate within a legal framework, and require legal principles and concepts that influence policy and limit choices. To be sure, the United States derives benefits from international legal rules and agreements with other states. Legal rules keep international society functional, contribute to economic order and political stability, and provide a basis for common ventures and mutual intercourse. Given that international law serves to limit the actions of all governments, it therefore enhances the security and independence of the United States in its dealings with other states. International legal rules establish common standards where they are deemed by states to be desirable and make more predictable what behavior to expect from states in their relations with each other. That is no less true for the United States in this age of globalization and increasing interdependence.
But international law also limits the freedom of the United States to act in its foreign affairs. The United States is obligated to certain restraints, irrespective of what its government might like to do when the time comes to act. Political arrangements legitimized by formal agreements are more difficult to unravel or modify. The predictability of state behavior established by international law means that the United States is not free to be disorderly or promote changes on its own whim. To foster the security and independence of its own territory and limit the conduct of other governments, the United States must accept corresponding limitations on its own behavior. To secure the confidence accrued from law, the United States must consent to being restricted in its ability to frustrate the expectations of other states. U.S. foreign policy therefore evolves in tandem with how international legal rules are regarded. Each successive administration builds its foreign policy on the legal framework constructed by its predecessors. Since World War II, U.S. foreign policy has moved slowly but perceptibly away from pragmatic, nationalist principles toward a more legalist, international doctrine. With the end of the Cold War, this tendency has accelerated. In the early twenty-first century, U.S. foreign policy was moving toward more universal values, bound by increasing legal commitments in formal multilateral agreements.
For American foreign policy, international law is most effective in regulating the rapidly expanding range of functional relations between the United States and other international actors. Such functional interstate relations are considered to be "low politics" (trade, communications, rules of diplomacy) and are motivated by a combination of idealism, moralism, and pragmatism. National security issues, however, retain their critical importance as pragmatic considerations, though increasingly the tendency has been to negotiate arms control agreements whenever possible, as opposed to seeking a straightforward balance of power amongst military adversaries. For the United States the restraint of legal rules appears least effective when applied to "high politics," meaning its national security relations between sovereign states. Under these circumstances, realism and pragmatism are prone to fostering American unilateralism in foreign dealings. Yet the wide range of arms control agreements, environmental regulations, and rules for war negotiated through U.S. leadership suggests that recourse to international legal solutions to deal with "high politics" issues retains great sway for U.S. foreign policy as well.
The American experience demonstrates that international law best serves those who make it work over the long term. As the body of rules for the international relations game, international law provides the formal ways and means for communicating to U.S. policymakers the perceived international consensus on policy questions and legal issues. Thus, the United States employs international law in its foreign policy and contributes to its creation. This explains why, with few exceptions, the United States formally recognizes and agrees to respect fundamental rules and principles intended to guide its foreign policy behavior. For the preeminent actor in international relations at the dawn of the twenty-first century, it cannot be otherwise.