UN Charter Article 2(4)

Article 2(4) is the bedrock of the post-World War II international order. The prohibition on the use of force against territorial integrity is considered jus cogens — a peremptory norm of international law from which no derogation is permitted. When the UN Charter entered into force in October 1945, it replaced the prior framework of the League of Nations and codified a categorical rule: states that launch unprovoked military attacks against other states violate the supreme law of the international community.

The only recognized exceptions are narrow: self-defense under Article 51 when an armed attack has actually occurred, and collective security action authorized by the UN Security Council under Chapter VII. Absent those, any use of force — including air strikes, ground invasions, naval blockades, or proxy warfare — that targets another state's territorial integrity or political independence is prohibited. The General Assembly's 1974 Definition of Aggression (Resolution 3314) further enumerates specific acts that constitute aggression under Article 2(4).

Critics note that the Security Council's veto structure — held by the five permanent members — can paralyze the UN's enforcement mechanism when one of those powers is itself the aggressor. This structural weakness does not negate the legal prohibition, however; it merely shifts accountability to other forums including the International Court of Justice, the International Criminal Court (for individual criminal liability), and the court of international public opinion.