The primary purpose of U.S. public diplomacy is to explain, promote, and defend American principles to audiences abroad. This objective goes well beyond the public affairs function of presenting and explaining the specific policies of various administrations. Policies and administrations change; principles do not, so long as the United States remains true to itself. Public diplomacy has a particularly vital mission during war, when the peoples of other countries, whether adversaries or allies, need to know why we fight. After all, it is a conflict of ideas that is behind the shooting wars, and it is that conflict which must be won to achieve any lasting success.