Political realism remains a powerful theoretical framework for thinking about international relations, including the war on terrorism. For Morgenthau and other realists, foreign policy is a matter of national interest defined in terms of power. Some writers view this tenet as weakening, if not severing, realism's link with morality. I take up the contrary view that morality is embedded in realist thought, as well as the possibility of realism being thinly and thickly moralised depending on the moral psychology of the agents. I argue that a prima facie case can be made within a thinly moralised realism for a relatively weak ally like Bosnia to enter the war on terrorism. An inflationary model of morality, however, explains how the moral horror of genocide in an ally's past may lead to a thickened moralised realism such that allied policy-makers question their country's entry into the war.