Does the United States need international law? At times in recent years, it has acted as if it does not. Yet international law provides the foundation not only for momentous undertakings, such as the efforts to halt the spread of nuclear weapons and to protect the ozone layer, but also for more routine endeavors, such as defining the boundaries of territorial seas and guaranteeing the right of diplomats to move freely. The United States needs international law acutely now because it offers a way to preserve our power and pursue our most important interests while reassuring our friends and allies that they have no reason to fear us or to form alliances as a counterweight to our overwhelming might. And we will need the law more than ever in the future, to regulate the behavior not only of states but of the individuals within them.
International law is not some kind of abstract end in itself. It's a complex of treaties and customary practices that govern, for example, the use of force, the protection of human rights, global public health, and the regulation of the oceans, space, and all other global commons. Each of its specialized regimes is based in the consent of states to a specific set of rules that allow them to reap gains from cooperation and thereby serve their collective interests. Overall, the rule of law in the global arena serves America's interests and reflects its most fundamental values. But in many specific areas, existing rules are too weak, too old, or too limited to address current threats and challenges. The United States must recommit itself to pursuing its interests in concert with other nations, according to principles of action that have been agreed upon and that are backed by legal obligation, political will, and economic and military power. At the same time, it has every right to insist that other nations recognize the extent to which many rules must be revised, updated, and even replaced.
International law provides the indispensable framework for the conduct of stable and orderly international relations. It does not descend from on high. Rather, it's created by states to serve their collective interests. Consider, for instance, the concept of sovereignty itself, which is routinely described as the cornerstone of the international legal system. Sovereignty is not some mysterious essence of statehood. It is a deliberate construct, invented and perpetuated by states seeking to reduce war and violence in a particular set of historical circumstances.
The founding myth of modern international law is that the Treaty of Westphalia, which ended the Thirty Years' War in 1648, gave birth to the system of states and the concept of inviolable state sovereignty. The Thirty Years' War was the last of the great religious wars in Europe, which were fought not really between states as such but between Catholics and Protestants. As religious minorities in one territory appealed to the coreligionist monarch of another, the Continent burned for three decades, and its people bled in a series of battles among the Holy Roman Empire, France, Sweden, Denmark, Bohemia, and a host of smaller principalities. The Treaty of Westphalia restored the principle of cuius regio eius religio--that is, the prince of a particular region determines the religion of his people. In today's language, this means that one sovereign state cannot intervene in the internal affairs of another.
But in reality, it took centuries for the modern state system to develop, and absolute sovereignty has never existed in practice, as many states on the receiving end of great-power interventions would attest. The architects of the Treaty of Westphalia glimpsed a vision of a world of discrete states armored against one another by the possession of "sovereignty"--a doctrine of legal right against military meddling.
It's important to realize that the right of sovereignty did not mean the prohibition of war. States were still free to go to war, as a matter of international law, until the Kellogg-Briand Pact of 1928 formally outlawed war (to evidently little effect). …