## Facts

- Nicaragua instituted proceedings alleging the United States organized, financed, trained, armed, and supported the Contras and conducted direct operations against Nicaragua, including mining ports and attacking infrastructure.
- Nicaragua invoked jurisdiction based on reciprocal optional-clause declarations and the 1956 Treaty of Friendship, Commerce and Navigation (FCN Treaty).
- The Court ordered provisional measures requiring the United States to cease actions restricting access to Nicaraguan ports, including laying mines, and to respect Nicaragua’s sovereignty and political independence.
- In the jurisdiction and admissibility judgment, the Court upheld jurisdiction under (i) Nicaragua’s continuing acceptance of compulsory jurisdiction and (ii) the United States’ 1946 declaration; it rejected efforts by the United States to exclude disputes with Central American states from pending or existing disputes and recognized an additional basis in the FCN Treaty.
- The United States later declined to participate further in the merits phase; the Court proceeded under its rules governing non-appearance and relied on documentary material and testimony to test the factual and legal basis of the claims.
- On the merits, the Court found U.S. authorization and execution of covert mining in or near Nicaraguan ports without warning to shipping, causing injury and damage, as well as other direct actions (including overflights and attacks on targets).
- The Court also addressed U.S. economic measures, distinguishing economic pressure from the legal category of “use of force,” while still evaluating alleged coercion under non-intervention principles.
- The United States asserted justification under collective self-defense, alleging Nicaragua supported insurgents in neighboring states.

## Issues

1. Whether the Court had jurisdiction and Nicaragua’s application was admissible notwithstanding U.S. reservations and attempted modifications to its optional-clause declaration.
2. Whether U.S. support for the Contras and direct military operations violated customary international law prohibiting the use of force, requiring non-intervention, and protecting state sovereignty.
3. Whether U.S. conduct was justified as collective self-defense, including whether an “armed attack” occurred and whether necessity and proportionality were satisfied.
4. Whether U.S. actions breached the 1956 FCN Treaty’s protections for commerce and navigation.
5. Whether, and to what extent, customary international law could be applied alongside treaty rules where treaty-based jurisdiction was contested or limited.

## Decision

- The Court held it had jurisdiction and the application was admissible; Nicaragua could rely on the United States’ optional-clause declaration, and the FCN Treaty supplied an additional jurisdictional basis.
- The Court determined the United States violated customary international law by using force through mining Nicaraguan ports and by supporting and directing military and paramilitary operations against Nicaragua (including training, arming, financing, and supplying the Contras).
- The Court held the United States violated the customary principle of non-intervention by coercive interference directed at influencing or overturning Nicaragua’s governmental policies.
- The Court found violations of Nicaragua’s sovereignty through actions affecting Nicaraguan territory, airspace, and waters, including unauthorized overflights and port mining.
- The Court found U.S. conduct relating to guidance and encouragement of Contra operations breached minimum humanitarian law obligations by encouraging prohibited practices.
- The Court rejected collective self-defense because the required conditions were not met, including insufficient proof of an armed attack attributable to Nicaragua, lack of a clear request by an alleged victim state, and failure to show necessity and proportionality.
- The Court held certain conduct, including interference with shipping and port mining, breached the FCN Treaty’s protections of freedom of commerce and navigation.
- The Court ordered the United States to cease unlawful acts and make reparation for injury caused; quantification was left for later proceedings.

## Legal Principles

- A respondent’s non-appearance does not grant default victory to the applicant; the tribunal must independently verify that claims are well founded in fact and law and evaluate the evidentiary record.
- The prohibition on the use of force and the principle of non-intervention exist as customary international law and may be applied alongside parallel treaty formulations; overlap with treaty text does not extinguish the customary rule.
- Not all unlawful uses of force qualify as an “armed attack”; only the most serious forms trigger the right of self-defense under customary law and the Charter framework.
- Collective self-defense requires (i) an armed attack against a state, (ii) a request or clear invocation by the victim state, and (iii) defensive measures that are necessary and proportionate.
- Intervention is unlawful when it is coercive with respect to matters reserved to a state’s free choice under sovereignty, including political system and external alignments.
- A state may incur responsibility for its own conduct in organizing, supporting, directing, or assisting unlawful operations even if all acts of a non-state proxy are not attributable to it as acts of the state.
- Interference with international shipping and commerce can violate treaty obligations protecting commerce and navigation, in addition to customary limits on force and sovereignty violations.

## Conclusion

The Court upheld jurisdiction over Nicaragua’s claims and, on the merits, held the United States responsible for unlawful uses of force and coercive intervention through direct attacks and extensive support to armed opposition forces, rejected collective self-defense for failure to satisfy its conditions, found additional treaty breaches affecting commerce and navigation, and ordered cessation and reparation.


Military & Paramilitary Activities in & Against Nicaragua (Nicar. v. U.S.), 1984 I.C.J. 392