Demon power has to do with the worship of other gods. The beginning was when Lucifer the fallen angel said that he would exalt himself....Isaiah 14:13. He desired to be worshiped, so he caused rebellion in heaven.
This same Lucifer/devil/satan deceived Eve in the Garden of Eden, causing Adam and Eve to be expelled from the Garden by God. Throughout the centuries, he has fought to be worshiped and to destroy all who loves the true and living God.