The person who, for his own purposes, brings on his land and collects and keeps there anything likely to do mischief if it escapes, must keep it at his peril; and … is prima facie answerable for all the damage which is the natural consequence of its escape.
—Lord Blackman. Rylands v Fletcher (1868) LR 3 HL 330.
Retribution in war is founded on the doctrine of collective responsibility. The guilty population is being punished for the actions of its agents. Just as a drunk driver cannot claim exculpation because he has no control over his affairs, nor can a despotically ruled people seek to excuse themselves on the grounds they have no control over their leader. They have a moral duty to maintain control over their affairs, to re-establish control over their own affairs if it is lost, and are responsible for the damage done to other peoples in the meantime.
Retribution provides a lesson to future generations and thereby enhances the future credibility of deterrence. Prior to World War II, the Axis powers considered the Anglo-Americans soft because of their aversion to war. They thought they could murder and intimidate them with impunity. The subsequent bombing of the German and Japanese cities showed the German and Japanese people the stupidity of their leaders and their folly in being led by them.
The horrific lesson meted out to the Germans and Japanese no doubt exercised the minds of the Soviets during the Cold War. They had no illusions as to the nature of Anglo-Americans and how they would react to aggression in Western Europe. Soviet understanding prevented the outbreak of World War III, and thus the suffering of the Japanese and Germans saved the lives of billions in the later decades of the twentieth century.
The punishment meted out to the wrongdoers in World War II, and the lesson that aggression has profoundly regrettable consequences, remains the wisdom of the world. As soon as aggression goes unpunished, however, the lesson will be unlearned. Aggressors will classify what happened in World War II as belonging to another age, no more likely to be repeated than some atrocity from classical times. Once that mindshift occurs, the credibility of deterrence, even nuclear deterrence, will be fatally undermined. That was why it was so important for the Argentineans to be forcibly removed from the Falklands in 1982 and the Iraqis from Kuwait in 1991. Yet both responses failed to properly punish the aggressors and thereby sent a tacit message to future would-be aggressors that the rules have now changed. In the future, if you invade another country, the worst that can be expected is to be evicted. Happily that unfortunate impression was rectified by the subsequent stretching of Saddam Hussein’s neck.