The point here is not whether NATO was justified but rather that it set a precedent. It broke with the tradition of national sovereignty that had prevailed since 1648, when the Treaty of Westphalia ended the Thirty Years War in Europe.

National sovereignty was further codified at the founding of the United Nations in 1945. Three of the seven principles in its charter were about sovereignty. The UN and its member states would not interfere in the internal affairs of any nation.

Since Kosovo, a different concept has been gathering momentum.

Speaking to NATO troops at Skopje, Macedonia, last June, President Clinton said that "whether you live in Africa, or Central Europe, or any other place, if somebody comes after innocent civilians and tries to kill them en masse because of their race, their ethnic background, or their religion, and it's within our power to stop it, we will stop it."

In September, UN Secretary-General Kofi Annan declared a "new commitment to intervention." He told the General Assembly that "if states bent on criminal behavior know that frontiers are not the absolute defense, if they know that the Security Council will take action to halt crimes against humanity, then they will not embark on such a course of action in expectation of sovereign impunity."

This Doctrine of Intervention establishes a whole new category of righteous wars, but some wars are more righteous than others.

The world disapproved of the Russian slaughter in Chechnya but decided, in a practical flashback to the Westphalian model, that Russia was too dangerous to challenge.

In early December, Russian Prime Minister Vladimir Putin warned the world against "interfering into affairs of independent states," and President Boris Yeltsin reminded us that Russia has nuclear weapons.

In similar fashion, China said that national sovereignty and noninterference are "the basic principles governing international relations." It remains to be seen whether the world will help Taiwan if China attacks.

The Doctrine of Intervention reached its present position mainly on the wings of moral justice. That is a notoriously subjective standard. Depending on how it is interpreted and applied, the dividing line between "just intervention" and aggression can be uncomfortably thin.

In 1938, Hitler used the grievances of ethnic Germans to justify his seizure of the Sudetenland from Czechoslovakia. The Russians claim to see a parallel between Chechnya and Kosovo.

Even those who support the concept of just intervention disagree on how to define it. Kofi Annan complains, for example, that "in Kosovo, a group of states intervened without seeking authority from the United Nations Security Council."

Had the proposed action against Yugoslavia come before the Security Council, it would have been vetoed by Russia and probably by China.

The chief prosecutor of the UN war crimes tribunal disclosed in December that she was evaluating evidence compiled by her staff that NATO commanders and pilots may have violated international law in conducting airstrikes against Yugoslavia. Press reports of the investigation led to its sudden termination.

Civil war is a major fact of life around the world. According to the US Institute of Peace, about 95 ethnic groups are involved in some sort of violent conflict. The current total of refugees is 21.5 million. Indonesia's violent suppression of East Timor last August made headlines, but most of us have never heard of conflicts like the one in Sri Lanka that has claimed 60,000 lives so far. Intervention in more than a fraction of these struggles is not possible. In a culture that supposes there is a solution to every problem, this is a difficult proposition to accept.

For good reason, the United States resists the role of global policeman. Nevertheless, when the international community acts--or when it doesn't--a special responsibility seems to accrue. In December, a UN report faulted the UN in general and the US in particular for not stopping the genocide in Rwanda in 1994.

We are walking more or less in step with Kofi Annan down a perilous path. By the very nature of it, interventionism raises the probability that we will be engaged in armed conflict. At the same time, it stimulates changes in the global balance of power. It has, for example, pulled Russia and China closer together.

For some advocates, though, the declared Doctrine of Intervention does not go far enough. Bernard Kouchner, the UN governor of Kosovo (and a founder of Doctors Without Borders) said in October that "now it is necessary to take the further step of using the right to intervention as a preventive measure to stop wars before they start and to stop murderers before they kill."

There will come times when intervention is inevitable, but we should curb our enthusiasm for making it a wholesale practice.

It behooves us to be careful, and to pick our interventions on the basis of where our national interests lie. It would also be a mistake to shed the last vestiges of the Westphalian model unless we have a solid replacement in hand.