How can peace be realized in the modern world? And how can Japan ensure its own security? Despite the intense debates over Japan’s recent security-related legislation, such vital issues as these were never explored. To give proper consideration to these thorny questions, it is indispensable to have both a knowledge of history indicating the circumstances in which wars occur and a real recognition of the security environment of the twenty-first century. This work explores hotly debated security-related matters from a standard viewpoint on international politics and diplomatic history. It also advocates in a bold yet level-headed manner the form Japan’s security should take and the path Japan should follow to make that a reality.