Law, College of


Date of this Version



Harvard Journal of Law & Public Policy 25 (2001), pp. 559-590


When representatives of fifty countries assembled in San Francisco in 1945 to draw up the United Nations Charter, modem threats of terrorism such as those posed by the Al Qaeda terrorist network were not yet known. The devastation caused by the September 11 terrorist attacks on the United States would not, however, have been an unfamiliar spectacle to the survivors of World War II. The "inherent" right of self-defense in responding to such violent attacks, a right enshrined in Article 51 of the U.N. Charter and understood by the delegates of all states as a long-established principle of customary international law, was a familiar concept in 1945.1

It was in accordance with these long-established principles of customary international law and Article 51 that the United States Government reported in a letter to the U.N. Security Council on October 7, 2001, that it had "initiated actions in the exercise of its inherent right of individual and collective self-defense following the armed attacks that were carried out against the United States on 11 September 2001."2 The letter went on to note that since the September 11 attacks, the U.S. Government had obtained "clear and compelling information that the al-Qaeda organization, which is supported by the Taliban regime in Afghanistan, had a central role in these attacks" and that United States armed forces had initiated actions "designed to prevent and deter further attacks on the United States" including "measures against al-Qaeda terrorist training camps and military installations of the Taliban regime in Afghanistan."3

The letter of October 7, 2001 was not the first time the United States has notified the U.N. Security Council of actions involving the use of force against other states and has invoked its inherent right of self-defense in response to terrorist attacks. As discussed below, previous uses of force by the United States against terrorist-supporting states have received varying responses from the international community, given rise to some criticism, and raised a number of international legal questions involving the right of guaranteed self-defense under Article 51 of the U.N. Charter. In contrast, the unprecedented response of the international community to the September 11 terrorist attacks on the United States and important factual and legal distinctions between the circumstances surrounding the September 11 attacks and previous attacks giving rise to the use of force by the United States, demonstrate the propriety of the exercise of self-defense in this case under the U.N. Charter and customary international law.