## Facts

- Nicaragua filed an application in April 1984 alleging the United States engaged in military and paramilitary activities against Nicaragua.
- Alleged conduct included organizing, training, arming, equipping, financing, and supplying the contra forces and encouraging operations to overthrow the Nicaraguan government.
- Nicaragua also alleged direct U.S. military actions, including mining Nicaraguan ports, attacking installations, violating airspace, and interfering with peaceful maritime commerce.
- Nicaragua asserted violations of customary international law and treaty obligations, including the U.N. Charter and a 1956 bilateral friendship, commerce, and navigation treaty.
- The United States issued a notification purporting to exclude disputes involving Central America from its optional-clause acceptance shortly before Nicaragua filed.
- In May 1984, the court indicated provisional measures directing the United States to cease actions restricting access to Nicaraguan ports, including laying mines, and to respect Nicaragua’s sovereignty and political independence.
- In November 1984, the court held it had jurisdiction and that the application was admissible under optional-clause declarations and, independently, under the bilateral treaty’s dispute-settlement clause.
- In January 1985, the United States ceased participation; the merits proceeded under the court’s non-appearance procedure, with the court requiring proof of Nicaragua’s claims in fact and law.

## Issues

1. Whether the court had jurisdiction and the application was admissible despite the United States’ attempted exclusion of Central American disputes.
2. Whether customary international law on the use of force, non-intervention, sovereignty, and self-defense could be applied independently of multilateral treaty provisions.
3. Whether U.S. conduct (including port mining, attacks, and support to the contras) breached customary rules protecting territorial sovereignty and prohibiting force and intervention.
4. Whether the United States could justify its conduct as collective self-defense, and what factual and legal conditions must be met for that defense.

## Decision

- The court upheld jurisdiction and admissibility, concluding the attempted exclusion could not remove jurisdiction over a pre-existing dispute and that a bilateral treaty provided an additional jurisdictional basis.
- Proceeding despite U.S. non-appearance, the court found the United States had engaged in unlawful uses of force, including mining ports and conducting attacks on Nicaraguan targets.
- The court held the United States violated the customary law principle of non-intervention by materially supporting and directing contra operations aimed at coercing Nicaragua’s internal political choices.
- The court found infringements of Nicaragua’s sovereignty and violations related to interference with peaceful maritime commerce.
- The court rejected collective self-defense, finding no adequate showing of an “armed attack” attributable to Nicaragua of the necessary scale and effects and no requisite declarations and requests for assistance by the allegedly injured states.
- The court ordered the United States to cease and refrain from the unlawful acts and to make reparation for injury caused.

## Legal Principles

- A state violates customary international law when it uses force against another state, including by direct military operations such as mining ports or attacking targets.
- Customary international law prohibits intervention, direct or indirect, in matters within another state’s domestic jurisdiction, including coercive support for armed groups seeking to change a government.
- The court may apply customary rules that correspond to treaty norms even when treaty-based adjudication is limited by jurisdictional reservations, so long as the case is resolved through custom rather than treaty interpretation as such.
- A distinction exists between an unlawful “use of force” and an “armed attack” that can trigger self-defense; assistance to rebels may be unlawful yet fall short of an armed attack.
- Collective self-defense under customary international law requires: (a) an armed attack against the victim state, (b) a declaration by that state that it has been attacked, (c) a request for assistance, and (d) necessity and proportionality.
- When a respondent does not appear, the court must still satisfy itself that the applicant’s claims are supported in fact and law and must scrutinize the evidentiary record before granting relief.

## Conclusion

The court held the United States responsible under customary international law for unlawful uses of force and prohibited intervention in Nicaragua, rejected collective self-defense for failure to meet required conditions, and ordered cessation and reparation.


Military & Paramilitary Activities in & Against Nicaragua (Nicar. v. U.S.), 1986 I.C.J. 14 (June 27)