The Lawful Resort to Unilateral Use of Force

A state may lawfully resort to unilateral use of force outside of its territory in the following circumstances: 1) When it has been subjected to an armed attack on its territory, vessels or military forces; 2) When the imminence of an attack is so clear and the danger so great that the necessity of self-defense "is instant (and) overwhelming;" 3) When another state that has been subjected to an unlawful armed attack by a third state requests armed assistance in repelling that attack; 4) When a third state has unlawfully intervened with armed force on one side of an internal conflict and the other side has requested counter intervention in response to the illegal intervention; or 5) When its nationals in a foreign country are in imminent peril of death or grave injury and the territorial sovereign is unable or unwilling to protect them.