The high ambition of the UN Charter Art. 2:4 to prevent interstate use of force is confirmed by the narrow right to individual or collective self-defence given to states under Art.51 ‘if an armed attack occurs’. States have many times invoked ‘self-defence’ as default justification of interventions and sometimes sought room for interpretations giving them more elbow room to use force in response to hostile acts of gravity. The general right of reprisal has been rejected, but in cases of grave or repeated terrorist attacks responses by armed force have not been criticized even though taken much after the attacks. A right has also been recognized to use force in self-defence where armed attacks are ‘imminent’ (pre-emption), but no such right has been acknowledged where the threat of attack is not imminent (‘anticipatory self-defence’ or ‘preventive’ use of force).