Have you ever heard of the Comanche? They are an offshoot of Shoshoni actually, they broke away from their heritage because they lost all spiritual belief. They lost their hearts and souls and they went dark. Not all but most. When they rode across the plains they became the terror of this country and multiplied quickly of all races. Indiscriminately they massacred without conscious, without fear or retribution, they tortured without thought. To them they could because they had no punishment for their actions here or in the afterlife. They chose their path in order to justify their works. "Blood Meridian" you should read it, most excellent book!