The past informs the future. For American foreign policy in the twenty-first century, this realization is critical for assessing what role international legal rules play in making and carrying out U.S. policy objectives abroad. The future of U.S. foreign policy still turns on the costs and advantages of three persistent conflicting impulses: the choices between isolationism and internationalism, realism and idealism, and intervention and nonintervention. International legal issues and concerns lie at the heart of each debate, and American policymakers bear the burden of reconciling these divergent viewpoints in rapidly changing global circumstances. The challenges for American foreign policy are daunting, particularly given the economic, political, and military superpower roles in which the United States is cast. The threats to U.S. security are no less menacing, among them: the proliferation of weapons of mass destruction; the degradation of the planet's environment through natural resource depletion; increased global warming, ozone depletion, and transnational pollution; pervasive poverty and overpopulation; terrorist violence; the rise of intrastate ethnic wars that produce genocidal atrocities and massive violations of human rights; accelerating forces of interdependence and globalization that make economic, technological, and electronic penetration of national borders increasingly facile; and the massive expansion in international commerce, which makes all states increasingly dependent on (and vulnerable to) others for needed goods and services.
The United States, despite its preponderant military, cultural, and economic power, cannot manage, much less mitigate, these global threats alone. Remedies lie in producing multilateral cooperation, collaboration, and commitment of mutual political wills among governments. The policy means for attaining these remedies come through active American diplomacy that strives to elaborate international legal strategies and agreements for meeting those ends. The conclusion is clear: international law is far from being an idealist pipe dream. International legal means are in fact realistic policy instruments that the United States must increasingly exercise if multilateral agreements are to be secured on common solutions and approaches for dealing with common global problems. In a world of intensifying interdependence and globalization, the United States needs international law to protect its fundamental national interests. Similarly, American foreign policy must be formulated in such a way that the United States accepts the norm of state responsibility to uphold its international legal obligations. To do otherwise is to ignore the lessons of U.S. diplomatic history and, more perturbing, to render the world an even more politically, economically, and ecologically complicated place in which to live.