Philip G. Zimbardo, The Lucifer Effect

When a power elite wants to destroy an enemy nation, it turns to propaganda experts to fashion a program of hate. What does it take for the citizens of one society to hate the citizens of another society to the degree that they want to segregate them, torment them, even kill them? It requires a “hostile imagination,” a psychological construction embedded deeply in their minds by propaganda that transforms those others into “The Enemy.” That image is a soldier’s most powerful motive, one that loads his rifle with ammunition of hate and fear. The image of a dreaded enemy threatening one’s personal well-being and the society’s national security emboldens mothers and fathers to send sons to war and empowers governments to rearrange priorities to turn plowshares into swords of destruction.