On human sacrifice by the Aztecs:

'What was the reason for all this carnage? Archaeologists will tell you the Mexica were reenacting their own creation myths, or that they genuinely thought that if they stopped sacrificing people to the rain god Tlaloc, he would stop sending rain. Or the sun would stop rising. Those of a more Marxist bent say that sacrifice was the way the ruling classes intimidated workers. All these explanations are plausible; none of them really satisfies. One Mexican archaeologist offered me all these theories and more before finally admitting, “I don’t know.” '
http://nautil.us/blog/we-may-never-truly-fathom-other-cultures

What if it was this process, out of control?