In King Leopold's Ghost, his classic expose of the ravages of colonialism in the Belgian Congo, Adam Hochschild responds to his own rhetorical question which asks how the soldiers could observe the beatings by those wielding the chicottes (a whip made from rhinocerous skin) and inflict pain and death on so many others.

First, he explains that these Africans workers were completely dehumanized, accorded the status of animals, by the prevailing racist beliefs of the time. Also, he says, these beliefs were strongly supported by the Belgian government of King Leopold, under whose authority they served.

For a white man to rebel meant challenging the system that provided your livelihood. Everyone around you was participating.

One example of a similar process of the dehumanization of an entire group of people since 1990 is Bashar al-Assad's genocide of his own Syrian population in the past decade. Included on the long list of his atrocities are torture, the use of outlawed chemical weapons, and the death of more than 500,000 Syrian citizens.