It [humanitarian intervention] is a universal duty. The obligation to stop a massacre falls on any state or coalition of states capable of acting effectively... State action of a forceful kind is required here. The goal is to stop the massacre and then help to install a non-murderous regime.
That's from a lecture by Michael Walzer at the NYU School of Law (for the quoted passage start 20 minutes in). Its subject is much broader, delineating the scope of global justice, as set against the ways of particular national communities - these being the necessary vehicles, within the minimal constraints of global justice, for securing a decent life for their citizens.
But I urge you to think about the forthright logic of the words of Michael's I have quoted. If humanitarian intervention is a universal duty of states when they can act effectively to save people from man-made calamity, then this entails that humanitarian intervention is also a right. For no state can have a duty to do what it has no right to do. If, consequently, there is (as some would have it) no right of humanitarian intervention even in the face of massacre and the like, there can be no general duty of it either. From which it would follow that people being massacred have to hope they'll be saved either by someone's benevolence or by the way things happen to fall out politically, for example at the UN. Otherwise, it's just tough luck. They aren't owed anything morally by the rest of the world. Embrace this morality those who want to. Me, I'm with Michael Walzer.
