Humanitarian intervention was supposed to have gone the way of the 1990s. The use of military force across borders to stop mass killing was seen as a luxury of an era in which national security concerns among the major powers were less pressing and problems of human security could come to the fore. Somalia, Haiti, Bosnia, Kosovo, East Timor, and Sierra Leone: these interventions, justified to varying degrees in humanitarian terms, were dismissed as products of an unusual interlude between the tensions of the Cold War and the new threat of terrorism. The events of September 11, 2001, supposedly changed all that by inducing a return to more immediate security challenges.