This says more about international law, however, than it does about the propriety of Israel's conduct. The rules of international law governing the use of force by victims of aggression are embarrassingly unjust and would never be tolerated by any domestic criminal law system. They give the advantage to unlawful aggressors and thereby undermine international justice, security and stability.
Article 51 of the U.N. Charter forbids all use of force except that for "self-defense if an armed attack occurs." Thus the United Kingdom's 1946 removal of sea mines that struck ships in the Strait of Corfu was held to be an illegal use of force by the International Court of Justice, even though Albania had refused to remove its mines from this much used international waterway. Israel's raid on Uganda's Entebbe Airport in 1976—to rescue the victims of an airplane hijacking by Palestinian terrorists—was also illegal under Article 51.
Domestic criminal law restricts the use of defensive force in large part because the law prefers that police be called, when possible, to do the defending. Force is authorized primarily to keep defenders safe until law enforcement officers arrive. Since there are no international police to call, the rules of international law should allow broader use of force by victims of aggression. But the rules are actually narrower.
Imagine that a local drug gang plans to rob your store and kill your security guards. There are no police, so the gang openly prepares its attack in the parking lot across the street, waiting only for the cover of darkness to increase its tactical advantage. If its intentions are clear, must you wait until the time the gang picks as being most advantageous to it?
American criminal law does not require that you wait. It allows force if it is "immediately necessary" (as stated in the American Law Institute's Model Penal Code, on which all states model their own codes), even if the attack is not yet imminent. Yet international law does require that you wait. Thus, in the 1967 Six Day War, Israel's use of force against Egypt, Syria and Jordan—neighbors that were preparing an attack to destroy it—was illegal under the U.N. Charter's Article 51, which forbids any use of force until the attack actually "occurs."
Now imagine that your next-door neighbor allows his house to be used by thugs who regularly attack your family. In the absence of a police force able or willing to intervene, it would be quite odd to forbid you to use force against the thugs in their sanctuary or against the sanctuary-giving neighbor.
Yet that is what international law does. From 1979-1981 the Sandinista government of Nicaragua unlawfully supplied arms and safe haven to insurgents seeking to overthrow the government of El Salvador. Yet El Salvador had no right under international law to use any force to end Nicaragua's violations of its sovereignty. The U.S. removal of the Taliban from Afghanistan in 2001 was similarly illegal under the U.N. Charter (although it earned broad international support).
An aggressor pressing a series of attacks is protected by international law in between attacks, and it can take comfort that the law allows force only against its raiders, not their support elements. In 1987, beginning with a missile strike on a Kuwaiti tanker, the Iranians launched attacks on shipping that were staged from their offshore oil platforms in the Persian Gulf. While it was difficult to catch the raiding parties in the act (note the current difficulty in defending shipping against the Somali pirates), the oil platforms used to stage the attacks could be and were attacked by the U.S. Yet these strikes were held illegal by the International Court of Justice.
Social science has increasingly shown that law's ability to gain compliance is in large measure a product of its credibility and legitimacy with its public. A law seen as unjust promotes resistance, undermines compliance, and loses its power to harness the powerful forces of social influence, stigmatization and condemnation.
Because international law has no enforcement mechanism, it is almost wholly dependent upon moral authority to gain compliance. Yet the reputation international law will increasingly earn from its rules on the use of defensive force is one of moral deafness.
True, it will not always be the best course for a victim of unlawful aggression to use force to defend or deter. Sometimes the smart course is no response or a merely symbolic one. But every state ought to have the lawful choice to do what is necessary to protect itself from aggression.
Rational people must share the dream of a world at peace. Thus the U.N. Charter's severe restrictions on use of force might be understandable—if only one could stop all use of force by creating a rule against it. Since that's not possible, the U.N. rule is dangerously naive. By creating what amount to "aggressors' rights," the restrictions on self-defense undermine justice and promote unlawful aggression. This erodes the moral authority of international law and makes less likely a future in which nations will turn to it, rather than to force.
Mr. Robinson, a professor of law at the University of Pennsylvania, is the co-author of "Law Without Justice: Why Criminal Law Does Not Give People What They Deserve" (Oxford, 2006).