I know in the 30ies when the Nazis buiolt their SA gangs to fight the communists and socialists they told the young men horror stories about their enemies. What they would do if they could, how they rape women, torture their prisoners ... . After that those men were so scared that they were happy to be in a SA brigade and willing to do to their enemies exactly the same things they heard before. Same thing happened over and over, for example in Bosnia. So the motivation is fear, caused by propaganda