Here's some facts on the Amazon civilization that may be useful later on

Also, an idea of the civilizations could be that the biomancers built up great control that had the entire Amazon under the rule of one person for a while, and then that person's death. This individual built up the defenses to the point that no foreigners wish to enter the Amazon. However, after this individuals death, the empire splits among the advisers/generals/friends. Think of Alexander the Great.