Jus ad bellum

Jus ad bellum is the body of international law governing when states may resort to armed force. The modern framework generally prohibits force, subject to narrow exceptions.

United Nations Charter Article 2(4): A provision of the UN Charter requiring states to refrain from the threat or use of force against another state’s territorial integrity or political independence. It establishes the modern baseline prohibition that resort-to-force claims must address.
Sovereignty: A state’s authority over its territory and independence from external control, subject to international law. The prohibition on force protects states’ territorial and political independence.
Treaty of Westphalia: The 1648 peace settlement that ended major European conflicts and helped establish principles of territorial sovereignty. Its sovereign-state order shaped the system later governed by rules on interstate force.
Nicaragua v. United States: A 1986 International Court of Justice case addressing U.S. support for armed groups and the law of force. The Court clarified the armed-attack threshold and limits on collective self-defense.
Anticipatory self-defense: The use of force before an armed attack occurs, justified as necessary to prevent an imminent attack. States disagree over whether the Charter permits force against threats that have not yet materialized.
Self-defense: A legal justification for defensive action against an armed attack, recognized in international law and domestic legal systems. It is the principal unilateral exception to the prohibition on interstate force.
Use of force in international law: The body of international law regulating states’ resort to force and related coercive measures. Jus ad bellum is the central framework within this broader legal subject.
Kellogg–Briand Pact: The 1928 treaty in which parties renounced war as an instrument of national policy. It marked a major pre-Charter attempt to outlaw war, despite weak enforcement.
Oil Platforms case: A 2003 International Court of Justice judgment on U.S. attacks against Iranian oil platforms during the Iran–Iraq War. The Court examined evidence, necessity, and proportionality in a self-defense claim.
Preemptive war: A war launched to forestall a perceived future threat that is not necessarily imminent. It tests whether preventive action can fit within the narrower law of self-defense.

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