At Agincourt in 1415, Henry V ordered a coup de grace for severely wounded French soldiers. Today, this would be a war crime: the laws of war mandate caring for the wounded and prohibit mercy killing. Defenders of the atomic bombings of Hiroshima and Nagasaki in August 1945 claim that for all their disastrous effects, these bombings were necessary to conclude the war and put an end to great suffering on both sides. Whatever one makes of these claims on their factual merits, the laws of war categorically forbid the intentional killing of civilians; Hiroshima and Nagasaki were indisputably war crimes. In 1990, some believed that Saddam Hussein should be assassinated so that the Iraqi and Kuwaiti people could be liberated from his oppressive rule without the need for a military invasion that would visit devastation on numerous people. Under the laws of war, the lawfulness of targeting a foreign leader outside of an ongoing armed conflict is dubious. Humanitarian interventions like the one undertaken by the United States and its allies in 1999 to stop the genocide in Kosovo are, by definition, designed to save lives. Humanitarian objectives make no difference under the laws of war, which generally forbid armed aggression across borders no matter what the reason.
The Laws of War and the "Lesser Evil",
Yale J. Int'l L.
Available at: https://digitalcommons.law.yale.edu/yjil/vol35/iss1/2