Self-Defense and the Use of Force in International Law

• In Event: Security at Home and Abroad

Abstract

Under international law, the only legal justification for using military force is self-defense in response to a prior act of aggression or armed attack. This is accepted by all states inasmuch as all are members of the United Nations, and none have ever renounced or even questioned the prohibition since it was implemented in 1945.
Yet the concept of self-defense can be ambiguous and encompasses a wide range of practices of varying severity, from armed reprisals, to air and naval bombardments, pre-emptive attacks, counter-attacks, and all-out war. Moreover, not all provocations constitute an armed attack for the purposes of evoking the principle of self-defense.
At the same time, even in cases of a clear provocation, the right to respond in not unlimited. The response must be reflective of the scope, nature and gravity of the attack and be limited to preventing further attacks. It may not be excessive, nor can it be directed at those who are not directly responsible for the initial provocation.
This paper will examine the legal options states have to respond to an act of aggression. It will argue that the legality of these responses, as well as the methods through which they are carried out, depends on two conditions: first, the nature of the initial action that triggered the response (its intensity, duration, and effect and whether it is likely to be repeated) and second, the degree to which the response follows the principles of necessity and proportionality.
I will apply these conditions to two contemporary conflicts.

Author

• Bruce Cronin, City College of New York