Customary International Law in the Nicaragua Case

Abstract

On 27 June 1986 the International Court of Justice passed judgment in the case concerning military and paramilitary activities in and against Nicaragua. Because of a reservation that the United States had made when it accepted the jurisdiction of the Court, the Court could not pronounce a decision regarding the dispute insofar as it concerned multilateral convertions. As a resuld of this, the Court was compelled to base its judgment largely on rules of customary international law and general principles of law. The rules of customary law which were relevant for the judgment corresponded to a significant extent, as regards their content, to the rules of treaty law which the Court was unable to apply, such as the prohibition on the use of force of Article 2, paragraph 4 of the Charter of the United Nations. This led the Court to indicate in precise terms how rules of treaty law and rules of customary law which have a corressponding content can co-exist and how the existence of rules of customary international law can be established in general. In addition, the Court examined in some detail the existence and content of certain specific rules of customary international law.