<P> Thus there is a right of self - defence under customary international law, as the International Court of Justice (ICJ) affirmed in the Nicaragua Case on the use of force . Some commentators believe that the effect of Article 51 is only to preserve this right when an armed attack occurs, and that other acts of self - defence are banned by article 2 (4). The more widely held opinion is that article 51 acknowledges this general right, and proceeds to lay down procedures for the specific situation when an armed attack does occur . Under the latter interpretation, the legitimate use of self - defence in situations when an armed attack has not actually occurred is permitted . It is also to be noted that not every act of violence will constitute an armed attack . The ICJ has tried to clarify, in the Nicaragua case, what level of force is necessary to qualify as an armed attack . </P> <P> The traditional customary rules on self - defence derive from an early diplomatic incident between the United States and the United Kingdom over the killing on some US citizens engaged in an attack on Canada, then a British colony . The so - called Caroline case established that there had to exist "a necessity of self - defence, instant, overwhelming, leaving no choice of means, and no moment of deliberation,' and furthermore that any action taken must be proportionate, "since the act justified by the necessity of self - defence, must be limited by that necessity, and kept clearly within it ." These statements by the US Secretary of State to the British authorities are accepted as an accurate description of the customary right of self - defence . </P> <P> There is a limited right of pre-emptive self - defence under customary law . Its continuing permissibility under the Charter hinges on the interpretation of article 51 . If it permits self - defence only when an armed attack has occurred, then there can be no right to pre-emptive self - defence . However, few observers really think that a state must wait for an armed attack to actually begin before taking action . A distinction can be drawn between "preventive" self - defence, which takes place when an attack is merely possible or foreseeable, and a permitted "interventionary" or "anticipatory" self - defence, which takes place when an armed attack is imminent and inevitable . The right to use interventionary, pre-emptive armed force in the face of an imminent attack has not been ruled out by the ICJ . But state practice and opinio juris overwhelmingly suggests that there is no right of preventive self - defence under international law . </P> <P> The controversial claim to a right to use force in order to protect nationals abroad has been asserted by some States . Examples include intervention by the UK in Suez (1956), Israel in Entebbe (1976) and the USA in the Dominican Republic (1965), Grenada (1983) and Panama (1989). The majority of States are doubtful about the existence of such a right . It is often claimed alongside other rights and reasons for using force . For example, the USA intervention in Grenada was widely considered to be in response to the rise to power of a socialist government . The danger that this posed to US nationals was doubtful and resulted in condemnation by the General Assembly . As with the above examples (except the Entebbe incident), the protection of nationals is often used as an excuse for other political objectives . </P>

Cases on the use of force in international law