This essay investigates the moral aspects of humanitarian intervention. Humanitarian intervention involves the balancing of at least three sometimes contradictory principles - the autnonomy of states, the prohibition of war and the reduction of harm and human suffering - and hence requires not merely a legal and political approach to the matter but renders a moral viewpoint necessary. It is argued that P.F. Strawson's concept Moral Reactive Attitudes (MRA) contributes to analysing the moral dilemmas and priorities involved. First, MRA underlines the moral aspects of international society that are essential for dealing with the moral conflict inherent in international society. Secondly, MRA helps to balance between competing claims of justification and legitimacy in cases of humanitarian intervention.