Article 2(3) and Article 33(1) require peaceful settlement of international disputes. Article 2(4) prohibits force or its threatened use.
Article 51 allows the "right of individual or collective self-defense if an armed attack occurs against a Member....until the Security Council has taken measures to maintain international peace and security."
Justifiable self-defense is permissible. Articles 2(3), 2(4), and 33 prohibit unilaterally threatening use of force not:
- specifically allowed under Article 51;
- authorized by the Security Council; and
- permitted by constitutional and US statute law provisions.
Three General Assembly resolutions prohibit non-consensual belligerence:
- the 1965 Declaration on the Inadmissibility of Intervention in the Domestic Affairs of States and the Protection of Their Independence and Sovereignty;
- the 1970 Declaration on Principles of International Law Concerning Friendly Relations and Cooperation among States in Accordance with the Charter of the United Nations; and
- the 1974 Definition of Aggression.
Nuremberg Tribunal's Justice Robert Jackson called aggressive war "the supreme international crime against peace." Guilty Nazi war criminals were hanged.