Draft – editorial review pending. As of 27 September 2026.

Nicaragua instituted proceedings against the United States on 9 April 1984 concerning military and paramilitary activities, including support for the contras, the laying of mines in Nicaraguan waters and attacks on ports and oil installations. In its 1986 merits judgment the Court applied customary international law, as the United States' multilateral treaty reservation prevented it from applying the UN Charter as such. The Court found that the United States had breached customary obligations not to intervene in the affairs of another State, not to use force against another State and not to violate its sovereignty. The judgment's statements on the prohibition of intervention, the use of force, armed attack, self-defence and attribution of conduct of non-State groups are referred to in debates on how international law applies to cyber and information operations. The United States did not participate in the merits phase after January 1985.

• Non-intervention (paras 202–209) – The Court described the principle of non-intervention as part of customary international law; prohibited intervention bears on matters in which each State is permitted, by the principle of State sovereignty, to decide freely, and is wrongful when it uses methods of coercion in regard to such choices (para. 205).
• Use of force and armed attack (paras 187–201) – The Court distinguished the most grave forms of the use of force (those constituting an armed attack) from other less grave forms (para. 191). An armed attack may include the sending by or on behalf of a State of armed bands if the operation, because of its “scale and effects”, would have been classified as an armed attack had it been carried out by regular armed forces (para. 195).
• Arming and training (paras 227–238) – Arming and training the contras was found to involve the threat or use of force, whereas the mere supply of funds was not, though it constituted intervention.
• Self-defence (paras 176, 194–195, 199) – Self-defence exists as a customary right subject to necessity and proportionality; collective self-defence requires that the victim State declare itself attacked and request assistance.
• Attribution (paras 115–116) – For the contras' violations to be attributed to the United States, it would have to be proved that the United States had “effective control” of the military or paramilitary operations in the course of which the alleged violations were committed.
• Psychological operations manual – The Court found that the United States, by producing in 1983 a manual on psychological operations in guerrilla warfare and disseminating it to the contras, had encouraged the commission of acts contrary to general principles of humanitarian law (operative para. 292).
• Economic measures (paras 239–245) – The Court did not consider the economic measures at issue to be a breach of the customary principle of non-intervention; certain measures breached the 1956 bilateral Treaty of Friendship, Commerce and Navigation.

The “scale and effects” formula (para. 195) and the description of prohibited intervention as coercive interference in matters within a State's domaine réservé (para. 205) are referred to in national positions on the application of international law in cyberspace and in expert works such as the Tallinn Manual 2.0 (tallinn_manual). States differ on how the coercion element applies to cyber operations and to influence or disinformation campaigns, for example in relation to electoral processes (see friendly_relations, ict_norms, germany). The “effective control” standard (para. 115) is referred to in discussions on attributing to States the cyber operations of non-State actors. The Court's finding on the psychological operations manual is referred to in discussions on State responsibility for information activities that encourage violations of international humanitarian law.

No recent developments recorded.

• charter
• friendly_relations
• ict_norms
• rome_statute
• ap1
• tallinn_manual
• germany

• ICJ, Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), case page, accessed 2026-09-27
• ICJ, Judgment of 27 June 1986 (Merits), accessed 2026-09-27
• ICJ, Summary of the Judgment of 27 June 1986, accessed 2026-09-27

• 2026-09-27: Entry created (draft).