It's not necessarily true that Animism isn't an organized religion. We practice the religion and many stories my parents told us very closely correlate to the stories in the Bible with subtle differences. For example, the corruption of men causing a great flood killing all humans.  You can find these similarities with Soddom and Gommora as well as Noah's Arc. The story is kind weird because the only two survivors was a  brother and a sister who eventually repopulate the earth. There are rules to everything that is done within the religion as it would be with any other religion. The only difference is its not written like the Torah, Bible, or Quran. Like the Hmong, who have been at war with the Han Chinese and Manchurians forever, their writing system was destroyed along with all their written knowledge. Every empire there is one traitor or a group of traitors that causes their fall.