Why must self-defense be necessary and proportionate under international law?

Under international law, the requirements of necessity and proportionality serve as essential ethical and legal constraints on the use of force, ensuring that military action remains a last resort rather than a tool for aggression or retribution.

• Necessity: This principle dictates that force may only be used when there is an instant, overwhelming need to act that leaves no other choice of means and no time for deliberation. It ensures that states do not resort to violence prematurely or when peaceful alternatives remain viable.12
• Proportionality: This principle requires that the force used must be commensurate with the threat faced. It prevents the escalation of conflict by limiting the scale and intensity of a military response to what is strictly required to neutralize the specific threat.12

These criteria are fundamental to distinguishing legitimate self-defense from illegal acts of reprisal, which are intended to punish rather than protect. By mandating these standards, international law seeks to uphold the ethical principle that the use of force must be minimized and strictly regulated to prevent unnecessary suffering and the uncontrolled escalation of global conflict.2134