Collective self-defence
recognises a right to collective self-defence. This allows a state to come to the aid of another state that has come under attack by a foreign power, in an exception to the prohibition on the use of force in international relations. Collective self-defence is enumerated as an inherent right in the Chapter VII, Article 51 of the Charter of the United Nations.
Concept
Collective self-defence refers to a situation in which one or more states take military action to assist another state that has come under attack by a foreign power. Chapter VII, Article 51 of the UN Charter enumerates an inherent right to both individual and collective self-defence, in an exception to the general prohibition on the use of force in international relations.Any legal exercise of the right to collective self-defence must meet two conditions: the state to be assisted must make a legitimate request for aid, and must have suffered an armed attack. No formal treaty need exist between the requesting state and the assisting state. The term "armed attack" refers to a "qualitatively grave use of force"; only a use of force of sufficient gravity can qualify as an armed attack. While the requesting state must have been subject to an armed attack for any exercise of collective self-defence to be legal, the assisting state need not have come under attack. As confirmed in Nicaragua v. United States, any exercise of collective self-defence must be both necessary – i.e. a last resort – and proportionate.