This obligation, as it applies to the acts of a single nation, and the rather restrictive exceptions to it are known as the rules on unilateral use of force. At the same time, there is the concept of collective security, which allows the community of nations to arise and oppose an aggressor nation together. This is regulated by the rules of collective security. Therefore, there are many situations where disputes between nations can break down into open conflict, and such conflict may still be completely legitimate under international law.
'All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of an State, or in any other manner inconsistent with the Purposes of the United Nations.'4
This builds on the preceding provision which places an obligation on Members to settle disputes peacefully5 which in turn follows from the very purposes and reasons for the United Nations, that being the maintenance of peace and security and the prevention and removal of threats thereto.6
De Arechega describes Article 2(4) as 'the cardinal rule of international law and the cornerstone of peaceful relations among States.'7 This altered the age-old rule, applying up till 1949, that us ...