The book before you is perhaps unusual in that it hopes to say something of interest to a number of discrete audiences: moral and political philosophers, international relations theorists, criminal and international lawyers—as well the general reader interested in the problems of war and violence. In part this is a result of my own interest in these various fields. More fundamentally, however, it reflects my belief in the interconnectedness of the issues under consideration. War, aggression, and violence are at once moral, legal, and political problems. Indeed the interplay between these different features is one of their most striking and challenging characteristics. Treating a single aspect of these problems in isolation can be useful in some respects, but it can also lead to sterile and unrealistic results. I believe that the best approach is often one which engages actively with the distinctive characteristics and literature of each facet of these problems.
The connections between law, politics, and morality are evident wherever one begins to think about the problems of war. From the moral point of view, it is a commonplace that, as Immanuel Kant stressed: 'ought implies can'. In other words, what one has a moral obligation to do is limited by what is possible—and this must include what is politically possible—in the circumstances. It follows that the ambitions, structure, and content of an account of international morality must be sensitive to what we know of the political constraints on state behaviour (though this observation is subject to an important proviso that I shall discuss below). On the other hand, what is politically possible in a given circumstance is itself affected by moral considerations. This is particularly true within the western democracies where leaders must justify to, and seek approval from, the public for their foreign policy—a public which is increasingly concerned about issues of justice and morality. So the relationship between moral discourse and politics is complex: one of a dynamic mutual engagement rather than a simple or outright conflict.
In this engagement between politics and morality the position of law, and in particular of international law, is of great importance and interest. International law represents an attempt to implement principles of justice within the sphere of politics. The content of international law is derived from international treaties and from