The essays in this book explore aspects of the conflict between isolationism and internationalism in American foreign policy formulation during the first forty years of the present century, the period in which the foreign policy of the United States came of age. Americans showed a marked degree of uneasiness in adjusting to the potentialities and dangers of the new position of the United States on the international scene. A growing feeling of insecurity seized the general public, leading it from the bold self-confidence of the turn of the century to the quasi-hysteria of the Cold War era. Over the period considered, we see at work, sometimes in extreme ways, two possible reactions to the solicitations coming in from abroad; a stubborn will to go back to nineteenth-century isolation and, conversely, an effort to master the course of events with new tools of international cooperation.