The international system imposes structural constraints on the ability of American decision makers to create legal rules favorable to U.S. national interests. The enduring feature of the international system is its decentralization. There are no central institutions to legislate standards or to ensure their enforcement. Nor does a common political culture exist in which to anchor an agreed-upon body of norms for governing the behavior of states. The upshot for U.S. foreign policy is a highly competitive international system in which there is constant expectation of violence and conflict and little expectation that either international law or appeals to normative principles will significantly influence the resolution of contentious issues.
A decentralized international system does not mean that U.S. foreign policy operates in a legal vacuum or under conditions of global anarchy. While there is no world government, and universally enforceable laws and common values are lacking, rules affecting the conduct of U.S. foreign policy do matter, and such rules lend greater predictability and more certainty to international transactions. These legal rules indicate the limits of permissible behavior, the norms for interstate conduct, and the ways and means of settling disputes. To the extent that the U.S. government subscribes to these legal rules, it becomes obligated to perform certain duties to those ends. That is, the United States as a sovereign, independent state is affected by legal principles contained in fundamental legal constructs. For its foreign policy to function the United States must be diplomatically recognized by other governments. In its foreign affairs, the government must accept and exercise certain rights and duties under international law, which are motivated by pragmatism and reciprocity. These rights and duties ensure that governments can deal with one another in a systematic, orderly fashion. The United States has the rights, inter alia, to recognize other states and to secure its national territorial integrity, sovereignty, and independence, by forcible self-defense if necessary. The United States also has corresponding obligations, key among which are not to intervene militarily into the affairs of other states, not to pollute the air, water, or land such that it causes trans-boundary harm, and to abide by international agreements made with other states or international actors. Although constrained by the world system, the United States is able to perform critical legal functions that ensure its survival as a legal entity in interstate relations.
A second structural constraint flows from the fact that the world system is a self-help system. The United States, like all governments, ultimately relies upon itself to accomplish foreign policy objectives. To do otherwise risks being manipulated by other governments. Similarly, the self-help principle impresses upon U.S. officials the need to bring policy goals and national resources into balance. International law strives to facilitate that. The pursuit of excessive goals, without adequate resources to attain them, can enervate a government and diminish its ability to respond effectively to future challenges. For the United States the tragedy of the Vietnam War remains a constant reminder of that truth.
A third structural constraint rests in the hierarchical character of the international system. The equality of states implicit in the legal principle of sovereignty is a political fiction. The notion of sovereignty dates back to the Treaty of Westphalia in 1648 and the origins of modern states. As a political construct, the sovereignty principle affirms that no legal authority exists above the state except that which the government voluntarily accepts. The reality of twenty-first-century international relations is markedly different. Sovereignty remains more a matter of degree than an absolute condition. States are inherently unequal, and the resources they use to exercise power in their international dealings are distributed unequally around the world. As the lone super-power state in the early twenty-first century, the United States has access to more resources, possesses greater capabilities, and can exercise greater power than any other state. In this context international law defines permissible ways and means that the U.S. government may employ those resources and capabilities in its foreign relations.
Despite systemic constraints, an international society does exist. International legal rules do affect the structure of that society—its institutions, actors, and procedures for transnational activity; the assumptions on which the society was founded; the status, rights, responsibilities, and obligations of states within this society; and the various relations between those states. Through its foreign policy the United States maintains, establishes, changes, and terminates relationships with other international actors—all through international legal means. Although international law may be primitive, the United States employs it to formalize, regulate, and regularize interstate relationships. For the United States most of the time, its foreign policy is constructed in a way that preserves international order, so that government policymakers might pursue the best perceived course for U.S. national interests, both foreign and domestic. Such international order depends on a framework of agreed presumptions, customs, commitments, expectations, and sanctions that all states, including the United States, accept to regulate international society. International law furnishes the rules for relations between states, sets standards for the conduct of governments within this international system, and facilitates establishment of multilateral institutions toward these ends. In these regards the United States has become the chief state architect and purveyor of international legal rules in the twenty-first century.