International terrorism carried out by nonstate actors and the spread of weapons of mass destruction (WMD) to dangerous states have emerged in recent years as the most significant security threats to the international order. Although the nature of the threats has changed dramatically, the legal regime governing the international use of force has not undergone a comparable transformation. Many commentators and strategists see a growing disconnect between states' security needs and the international law security architecture. Contending that the international law rules and international institutions established by the U.N. Charter are ill-suited to meeting contemporary security threats, these commentators and policymakers advance new doctrines to expand the entitlement of states to use force unilaterally in self-defense.

This Article rejects this perspective and the associated prescriptions for new legal rules to regulate the international use of force. It demonstrates that the U.N. Charter created a two-tiered system of rules and standards to govern the use of force. With respect to unilateral uses of force by states, the Charter employs a bright-line rule: to guard against erroneous and bad-faith invocations of the right of self-defense, force may be used unilaterally only in the event of an armed attack. The Charter employs a more flexible standards-based approach, subject to the procedural safeguards of collective decision-making by the Security Council, to authorize force to confront threats to international peace and security.

The Article challenges the widely held assumption that the competing interests of the Permanent Members will inevitably produce gridlock in the Security Council with respect to collective action against the new security threats. To the contrary, there is an underlying affinity of interests among the Permanent Members with respect to these threats. The Permanent Members all face major international terrorist threats, and they all seek to preserve their near-monopoly over WMD. Accordingly, the Permanent Members share an interest in confronting international terrorism and preventing the proliferation of weapons of mass destruction. Because these contemporary security threats-- unlike the rivalries of the Cold War era--do not implicate competing interests of the Permanent Members, the Security Council's security architecture is actually better suited to addressing today's threats than it was to countering the state-versus-state conflicts for which it was designed. The recent behavior of the Permanent Members reflects their increasing cooperation on the basis of this affinity of interests.

The Article further argues that the use of force pursuant to the Charter's collective security provisions carries with it greater legitimacy, greater prospect for success, and less danger of destabilizing error or abuse than would force exercised pursuant to doctrines that expand the right of states to use force unilaterally. The Article also identifies pragmatic policy and diplomatic steps the Permanent Members should take to build upon their underlying affinity of interests regarding international terrorism and WMD proliferation so as to strengthen the capacity of the collective security architecture to confront these threats.