Under what conditions is the use of force “legitimate”? This is a question that has had many
answers through the centuries. Force was once legitimate when used in a just cause according to Catholic doctrine, when used to expand an empire, or when used to unite a nation. The drama of the 20th century, from an international legal point of view, is the effort for the first time actually to outlaw the use of force except when used in self-defense, and to transfer the legitimate use of force to a multilateral institution. That is the signal legal achievement of the UN Charter, the structure created by the combination of Article 2(4), Article 51, and Chapter VII.
Today these rules need to be rewritten, or at least amended. The Charter rules were written for the last war – for a classic inter-state conflict waged by standing armies of identifiable soldiers. As horrific as the invasion of Poland or the attack on Pearl Harbor was, the world had time to respond before irrevocable damage was done, and time, indeed, to anticipate and forestall the attack by collective action. The most dangerous security threat facing nations in the 21st century is a possible terrorist attack using a nuclear or biological weapon capable of killing hundreds of thousands or indeed millions of people at a stroke.
Neither deterrence nor defense offer adequate protection against this possibility. We must instead be able to identify the would-be attackers and stop them before they can strike. President Bush has proclaimed a doctrine of unilateral preemption, whereby individual nations that perceive themselves to be at risk can strike first. Secretary General Kofi Annan has rejected unilateral preemption, but has nevertheless recognized the gravity and unprecedented nature of the threat and called upon the Security Council to consider “early authorization of coercive measures.”
Such authorization will require a revision or at least a reinterpretation of what constitutes a
“threat to the...