We will not fully understand the phenomenon of war – nor be as dexterous as we might in avoiding it – until we begin to appreciate the multidimensionality of its causes. This book demonstrates that the justice motive can contribute to the outbreak of war in a complex variety of ways, and that many wars that seem puzzling from a traditional Realist perspective emphasizing the motives of self-preservation and self-aggrandizement can be explained more satisfactorily once we appreciate the importance and the agency of moral motivations.

It seems likely that as a result of its failure to take these motivations seriously, political science has paid an enormous opportunity cost. Perhaps that cost might have been avoided if the scientific approach to international relations had supplemented, rather than rejected, the more humanistic tradition it displaced. Terry Nardin writes:

But the entrenchment of the scientific approach does not militate against the possibility of richer, more subtle, and more useful political science.