There were at least three major cultures that occupied Mesoamerica. Mayans, Incas and Aztecs. All three demanded war and sacrifice but only the last two were human sacrifice. Each died out as another rose and the last was conqured by the spanish. Natural causes were also that they expanded to fast and consumed more land and resources then the land could support. Think trees all gone so the farm land becasue desert and no food could grow. People left the cities for the forest because they could find food there. Try Wikipedia for more.
