Of all the problems of moral and political philosophy there are few as difficult or as urgent as those concerning war, aggression, and violence. They are, of course, very old problems but there are two features which make them particularly challenging. The first is that they concern what we might call 'morality in extremis'. In war and interpersonal violence we find humans at our most fearful, most vulnerable, and also most destructive. Because of this, the issues they raise are among the most intense, difficult, disturbing, and yet characteristically human of all moral problems. Secondly, the character and nature of these problems changes with evolving historical circumstance. This fact compels us to continually re-evaluate the principles and sometimes the very concepts of our moral assessment.
At the present time the legal and moral norms of war are under extraordinary strain. The strain has come from developments in many different areas: from new weapons and strategic realities (such as the development of terrorism and guerrilla warfare); from new forms of political association (such as the European Union) and in some cases disassociation (failed states and fragmenting multinational states); and from new moral and political priorities (such as the spectacular rise in the conception of universal human rights). All of these developments raise fundamental moral and legal questions. Among them are questions about the nature of responsibility and moral agency, the status and foundation of human and community rights, and the relationship between individual and state.
This book is an attempt to explore our moral response to war and aggression through the lens of a single idea—that of self-defense. In so doing I will hope to provide a little forward illumination as to how some of these issues might productively be tackled in the twenty-first century.
I have chosen to focus on self-defense for a number of reasons. The first is a deep dissatisfaction with the way the notion of self-defense is applied in international law and international ethics. Self-defense is first and foremost a feature of personal morality and criminal codes, but it has become one of the most important elements in our thinking about the rights and wrongs of international violence. Thus self-defense is central to modern international law: it is currently the sole legal justification for the use of force by states without the