This paper explores the international law governing the use of force in the wake of conflicts in Kosovo, Afghanistan, and Iraq. Developments since the conclusion of World War II, such as the emergence of international terrorism and rogue states and the easier availability of weapons of mass destruction, have placed enormous strain on the bright line rules of the UN Charter system. This paper argue that a more flexible standard should govern the use of force in self-defense, one that focuses less on temporal imminence and more on the magnitude of the potential harm and the probability of an attack. It further argues that the consensus academic view on self-defense - that force is justified only as a necessary response to an imminent attack - which was largely borrowed from the criminal law, makes little sense when transplanted to the international context. It concludes by questioning whether self-defense, grounded as it is in a vision of individual rights and liberties in relation to state action, is the proper lens through which to view the use of force in international politics. Rather than pursuing doctrinal or moral approaches, this paper addresses the rules governing the use of force from an instrumental perspective. It asks what goals the international system, and its most currently powerful actor - the United States - should seek to achieve with the use of force, and whether the current rules permit their pursuit. An approach that weighs costs and benefits to the stability of the international system, which could be seen as an international public good currently provided by the United States and its allies, might better explain recent conduct and provide a guide for future action.