The control of man's violence against man presents to modern society its greatest problem. A capacity to deal with the most devastating type of conflict -- international war -- is crucial to human welfare and even to the survival of civilization. Nations have become interdependent in technology and economy, but world political organization is based on a system of sovereign states now divided into hostile camps armed with absolute weapons. This book is a study of the development of collective security, or international cooperative action for the maintenance of peace. The approach is based upon the "principle of concern," a recognition of the fact that organization to preserve peace is essential for every political community. As a case study Willard N. Hogan has analyzed the principle of collective security as it has worked in practice in international organizations over the past thirty-five years. He holds that collective security is not unworkable as a method for stopping aggression and maintaining peace.