Demonising the enemy. Literally.

In every war, both sides demonise their enemy to depersonalise them and make it easier for their soldiers to pull the trigger. So in 1914, British troops were related stories of how German forces invading Belgium had raped nuns and tossed babies in the air so as to spear them on their bayonets, while in World War II the Germans were pictured as blond vikings standing against the evils of slavic Bolshevism. But neither is as literal as this example from a US Marine colonel, quoted by the BBC:

"The marines that I have had wounded over the past five months have been attacked by a faceless enemy," said Colonel Brandl.

"But the enemy has got a face. He's called Satan. He lives in Falluja. And we're going to destroy him."

Iraqis are Satan. Literally. No wonder the US doesn't give a rat's arse about civilian casualties when they're seeing horns and pitchforks through their gunsights.