Most of them are, but, not all of them.
Most religions are polytheistic, monotheistic, or particularistic. Some monotheistic religions are particularistic as are polytheistic. There are no religions that are all three.
It's untrue to say that they're all polytheistic.
Hindu?
polytheistic.
Back when Judaism was first Founded, all other religions were polytheistic. Judaism was monotheistic.
Animism is the belief that all plants and animals, or even all physical objects, have spirits. Some animists believe that collectively we are all part of the spirit of the cosmos creating itself.
Polytheistic religions.
There is not a full list alot of religions were in the PREHISTORY stage. So no one knows all of the polytheistic and monotheistic Religion's. The barbarians whom had no pacific religion. And if they did it was in prehistory. -Prehistory, a time before recorded history.
You say "the" polytheistic religion; however, you should note that there is not ONE polytheistic religion, but several different such religions. The only thing all have in common is that they believe in several gods.
All of those religions were polytheistic, except, perhaps the religion of the Israelites.
The people of Nigeria have numerous religions: Christian, Muslim, & animistic religions. As Christian or Muslim, they are monotheistic; Animistic believers would be polytheistic.
Polytheistic religion is the worship of many gods.