Given how catastrophic the invasion of Iraq has turned out to be, it is hard even to remember when interventions on moral grounds – whether to thwart a dictator, as in the case of the Balkan wars, or to put an end to anarchic cruelty, as in the case of British intervention in Sierra Leone – seemed like a great advance in international affairs. No longer would the powerful sit by idly while butchers like Slobodan Milosevic or Foday Sankoh slaughtered their own people.