Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America)

Facts

• Nicaragua brought proceedings against the United States, alleging the US had trained, armed, equipped, and directed Contra rebel forces against the Nicaraguan government
• The US had also mined Nicaraguan harbours
• The US denied ICJ jurisdiction and withdrew from proceedings after the jurisdiction phase
• The case proceeded on merits without US participation

Issue

1. Whether the ICJ had jurisdiction over the dispute, and whether the US violated customary international law by using force against Nicaragua and interfering in its internal affairs.

Held

• Jurisdiction upheld based on the Optional Clause declarations and a 1956 US-Nicaragua Treaty of Friendship
• The US violated customary international law by:
• Training and directing the Contras
• Mining Nicaraguan ports
• Directing attacks on Nicaraguan infrastructure

Ratio Decidendi

Customary international law and treaty law can co-exist on the same subject matter. The prohibition on the use of force is not merely a Charter obligation but an independent rule of customary law. Self-defence under customary law requires proportionality, necessity, and a request from the attacked state. The ICJ has jurisdiction even when a permanent Security Council member refuses to participate.