By Eric A. Posner

The execution-style killing of Muammar al-Qaddafi by a mob of gunmen in the ruins of Sirte last week put an end to NATO's six-month military intervention in Libya. Unless the country descends into anarchy or an equally abhorrent dictator succeeds Qaddafi, the Libya intervention will be regarded as a victory for the West, for the United States, and for that reluctant but surprisingly fierce warrior, President Barack Obama. And it's a victory that came on the cheap. It is rare thing indeed for the Pentagon to spend as little as $1 billion on a successful military campaign, without losing ten times that amount in the sofa cushions.

But if the Libya intervention turns out to be a political and moral victory, it also illustrates once again the motto, inter arma silent leges -- in times of war, the law falls mute. Both international and U.S. law took a drubbing alongside Qaddafi's ragtag army, casting further doubt upon the already tenuous notion that international military actions can be conducted on a legal basis.

The basis for the intervention under international law was dubious from the start. Libya is a sovereign state and, as a matter of international law, NATO cannot bomb it without a legal justification. The rebels' request for military intervention could not override the government's quite understandable, if regrettable, refusal to give its consent to be bombed. So, the United States and NATO turned to the U.N. Security Council, which enjoys the power under the U.N. Charter to authorize military interventions in foreign countries.

But two problems arose. The first was the legal justification for intervening. The Charter gives the Security Council authority to take actions to promote peace and collective security. But Libya did not threaten its neighbors or any other country. The purpose of the intervention, according to the resolution that authorized it, was to protect Libyan civilians from their government.

Some commentators claimed that the Libyan intervention was justified by the Responsibility to Protect (obnoxiously known as "R2P"), a principle formally endorsed by U.N. members in 2005. The Responsibility to Protect requires all countries to protect their own civilians, and may permit the international community to intervene if they do not. However, the Responsibility to Protect never achieved the status of international law because states were not willing to embody the principle in a binding treaty. As a principle or norm, it has been applied selectively, to say the least. No one seems interested in protecting Syrian or North Korean civilians from their governments. The truth is that the Responsibility to Protect is too capacious a norm to regulate states: It can be cited to justify virtually any intervention in the type of country that the West might want to invade, while it can also be evaded on grounds that it is not formal law, so countries can avoid intervening in a crisis when intervention does not serve their interests.

The second problem was procedural. The 15-member Security Council must authorize any military intervention by a three-fifths supermajority -- nine votes. The supermajority requirement poses few obstacles because smaller countries that rotate onto the Council can be easily bullied or bought off, but the permanent members -- the United States, France, Britain, China, and Russia -- possess vetoes. In 1999, China and Russia refused to consent to a military intervention in Serbia to protect Kosovo from ethnic cleansing, forcing NATO to go it alone and violate the law. In 2003, the United States and Britain invaded Iraq without Security Council authorization. Possibly realizing the limited power of their vetoes if Western countries could simply ignore them in the past, and recognizing that Arab states supported the rebels, China and Russia abstained this time, and an authorizing resolution was issued.

But China and Russia appear to have used their bargaining power to secure some concessions. Resolution 1973 did not authorize a full-blown ground invasion, and in fact prohibited a "foreign occupation force." Instead, it established a no-fly zone, and authorized the use of military force to "protect civilians and civilian populated areas under threat of attack." This was not a remit to depose Qaddafi.

Far from adhering to these essentially defensive parameters, NATO took an active part in assisting the rebels' campaign to overthrow the government, with some countries even sending limited ground forces, and undertaking various efforts to assassinate Qaddafi in bombing attacks. None of this was blatantly illegal -- and NATO could point out that protecting civilians required disabling Libyan ground forces and their leadership -- but it was far from the spirit of Resolution 1973, and of the U.N. Charter itself, which was never understood to give powerful states a means to bully small or medium-sized countries that did not comply with their visions of international order.

Another casualty of the military intervention was human rights. To be sure, Qaddafi was a cruel dictator, and his overthrow was a victory for those who care about human rights. But human rights law does not endorse the principle that the ends justify the means -- even if the ends are humanitarian. As Amnesty International reported, the rebel groups "abducted, arbitrarily detained, tortured and killed former members of the security forces, suspected Gaddafi loyalists, captured soldiers and foreign nationals wrongly suspected of being mercenaries fighting on behalf of Gaddafi forces."

That this would happen was surely obvious to the policymakers involved. That this would happen when NATO forces commit themselves to an air war, and refuse to send ground troops that might have imposed some discipline on the rebel forces, should have been even more obvious. But the fact is that a ground campaign was politically impossible. Thus, the choice was between non-intervention, which could have resulted in massacres and the prolongation of Qaddafi's regime, or intervention along with moral, if not necessarily legal, complicity in torture and crimes against humanity by the rebels. International law provides no guidance for making this tradeoff, and thus surely did not influence the decisions of the governments.

The denouement, some six months after the U.N. resolutions, continues the theme. International lawyers and human rights advocates insisted that Qaddafi be captured and tried for his international crimes, either in an international tribunal or in a domestic court that complied with exacting international standards. Indeed, the Security Council had referred the matter to the International Criminal Court, which indicted Qaddafi, his son Saif al-Islam, and brother-in-law and military intelligence chief Abdullah Senussi in June. The rebel forces appear to have executed Qaddafi without a trial, and one wonders whether they did so in part to avoid the nightmare of international criminal adjudication.

The International Criminal Court is a virtually untested institution. It has conducted a handful of trials over its ten-year existence; only one of them, that of former Congolese rebel leader Thomas Lubanga, is even close to completion. The ICC was supposed to replace the ad hoc tribunals that had been used for Rwanda and Yugoslavia, which were chiefly famous for the expense and length of their trials, and hence their very limited achievements in terms of international justice. For international lawyers and human rights advocates, the delays and ambiguity are a small price to pay for the catharsis of an international criminal conviction that would vindicate international law. For advocates, every international criminal trial is supposed to regularize and promote international law, so each trial helps establish a new international legal order. In pursuit of this utopian goal, advocates disregard the needs of the people they purport to help, which are put to the side for the sake of an imaginary future in which international law finally prevails over power.

What were these needs in Libya? It must have been obvious to Libyans that an endless international trial in a faraway country -- the Netherlands -- would not serve their immediate political needs, to say nothing of their sense of justice, which required death. (The ICC is not permitted to impose the death penalty since many countries -- including its main sponsors -- regard the death penalty as contrary to international law.)

A trial would have been pointless as well. In the real world, trials are designed to establish the truth; but who doubts that Qaddafi terrorized his people, and had to be removed from the scene if Libya was to move forward? The facts of his reign are not in dispute, but are also, in a way, irrelevant because no one wanted him to retain power. A grandstanding Qaddafi at trial over a course of years could hardly have contributed to political stability in Libya. Indeed, a Qaddafi who remained alive even for a short time after his capture may well have been a threat to stability. If the Libyan rebels executed Qaddafi to avoid this outcome, it was surely a sensible thing to do, whatever international law might require.

The irregularity of the Libya intervention from the standpoint of international law has a domestic counterpart: the illegality of U.S. military participation under U.S. law. Obama sent U.S. troops to war without congressional authorization and in violation of the War Powers Resolution, which requires the president to withdraw troops from "hostilities" if he does not secure congressional consent within 60 days of the start of hostilities. In June, the Justice Department advised Obama that he would have to withdraw American forces under the War Powers Resolution, but Obama disregarded this advice, relying instead on tendentious advice from elsewhere in the government that the bombing campaign in Libya, which ultimately involved more than 7,000 sorties involving U.S. aircraft, did not count as "hostilities," and thus did not trigger the resolution. A better explanation is that the War Powers Resolution is a dead letter. President Bill Clinton violated it as well in 1999 when Congress refused to authorize the intervention in Serbia -- and generally speaking presidents have given it only lip service since its enactment in 1973.

Both domestically and internationally, then, the dogs of war have escaped the well-meaning efforts to subject them to legal frameworks. When unpopular wars fall afoul of the law, policymakers and advocates believe themselves justified in redoubling their efforts to build up the law, so as to prevent a recurrence. A "good war" that runs afoul of the law, however, presents more significant obstacles, for it suggests that lawmakers are incapable of setting out rules that sensibly authorize the use of military force when it is warranted and restrain its use when it is not.

It is possible, indeed likely, that if countries had complied with international law, and the U.S. government had complied with domestic law, Qaddafi would still be in power, while thousands of Libyan civilians would be in torture chambers or graves. A similar conundrum confronted governments in the 1999 Serbia war, leading an international commission to declare that the war was "illegal but legitimate" -- a near contradiction which comes close to saying that governments should disregard law when they have, or think they have, legitimate moral or political aims. But given that governments always believe that their aims are legitimate, what force can law possibly have when it comes to arms?