On Killing by LtCol Dave Grossman, 2009, Excerpts
The social class structure that exists in the military provides a denial mechanism that makes it possible for leaders to order their men to their deaths. The class structure is even more pronounced in the British army. The influence of social distance has been very powerful in ages past, when all officers came from the nobility and had a lifetime’s experience in wielding the power of life and death.
In nearly all historical battles prior to the age of Napoleon, the serf who looked down his spear or musket at the enemy saw another hapless serf very much like himself, and we can understand that he was not particularly inclined to kill his mirror image. And so it is that the great majority of close-combat killing in ancient history was not done by the mobs of serfs and peasants who formed the great mass of combatants. It was the elite, the nobility, who were the real killers in these battles, usually in the pursuit phase after the battle, on horseback or from chariots, and they were enabled by, among other things, social distance.