The use of the blockade against Germany to starve large numbers of people to death broke through the moral barrier against the mass killing of civilians. It was the precedent for the 'conventional' bombing of civilians in the Second World War and then for the use of the atomic bomb.
Jonathan Glover, Humanity: A Moral History of the Twentieth Century
bombing, civilian-casualties, civilians, killing, morality, nuclear-bomb, world-war-ii