Why does international law prohibit weapons designed to cause unnecessary suffering?

International law prohibits weapons designed to cause unnecessary suffering based on the fundamental principle that the only legitimate objective of war is to weaken the military forces of the enemy. Because the right of belligerents to injure their opponents is not unlimited, international treaties—such as the Hague Convention of 1907 and the Declaration of St. Petersburg of 1868—explicitly forbid the use of arms, projectiles, or materials calculated to inflict superfluous injury or needless pain.1

This ethical framework reflects a humanitarian consensus that emerged alongside the development of modern weaponry and improved battlefield medical care. By restricting means of warfare that cause excessive harm, international law seeks to uphold basic principles of humanity even during armed conflict. Consequently, states are directed to evaluate whether any new weapons they develop might infringe upon these established legal rules, ensuring that military necessity does not override the moral imperative to minimize suffering.21