A recurrent debate at the center of U.S. foreign policy has pitted internationalists against isolationists. Internationalists favor an active role for the country in world affairs, including strong support for international institutions and a generally interventionist approach to problems in other countries. Many internationalists believe that America has a responsibility to participate in world affairs because of its unusual capacity to favorably alter global conditions. Other internationalists maintain that America simply cannot turn its back on a world in which it has become so deeply networked. Isolationists, by contrast, have consistently argued that overseas commitments can force the United States into actions best avoided, and that institutions such as the United Nations undermine American sovereignty. They contend that excessive attention to events in other countries both distracts from important domestic priorities and needlessly embroils the country in costly enterprises bearing little relation to the national interest. In...