The core text — Article 2(4): "All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the Purposes of the United Nations." The elements: (i) force (armed force — the Nicaragua case's holding on the definition's limits: the Article's debate on economic/political coercion excluded); (ii) threat as well as use (the threatened unlawful force); (iii) the protected interests — territorial integrity and political independence (read, per Nicaragua, as the situations protected, not loopholes: force against any state's territorial integrity violates the rule); (iv) the Purposes clause as catch-all. Article 2(3)'s companion — peaceful settlement of disputes (Unit 8's gateway).
The exceptions' closed architecture: (1) self-defence (Article 51); (2) collective security (Chapter VII); (3) the debatable residual: invitation (Unit 4) and the "hidden" loopholes contested (humanitarian intervention's claim — Unit 4). The Charter's hierarchy: force's monopoly in the Security Council — the members having "conferred on the Security Council primary responsibility" (Article 24).