Judaism
Multitudes of gods might have seemed to be the obvious way to explain the mysteries of nature, but it is not easy for priests to convince people to cooperate when their beliefs are based upon myths about gods behaving badly towards each other. And when different cities honor different gods, people just have one more excuse to kill each other.
With the onset of the Iron Age, while the moral development of every other nation in the Mediterranean region was being held back by myths about incestuous families of cruel and ambitious gods, the priests of Israel dared to take advantage of the newly discovered power of alphabetic writing to persuade their population to adopt a more refined level of superstition.
Using sober language, they crafted a detailed mythology, with a single god, a convincing creation myth, and a declaration of ten sacred commandments: Do not murder; Do not steal; Do not lie; and so on. Using a collection of myths about miraculous events, the priests had succeeded in uniting their people under a common belief and giving them a practical set of laws and values.
The people of Israel no longer needed such a strong central authority to enforce the laws. Whoever believed in the mythology would themselves become the law keepers. And rather than ruining the nation to satisfy their own ambitions, kings would be held accountable to the same standards of behavior as commoners.
The Jewish strategy proved to be so effective that the Greeks, Romans, and Arabs eventually followed their lead, convincing their own people to adopt a single moral god of creation by building upon the successful foundations of the Jewish mythology.
To the credit of the early Jewish prophets, they continued to focus on punishment for the wicked in this life, and were never desperate enough to allow their scriptures to descend to the level of threatening punishment in the next life. The early Jewish scriptures only ever said that when we die, “our dust returns to the earth as it was, and our spirit returns to God who gave it.”
As the centuries passed, additions were made to the scriptures to reinforce the better aspects of the religion. But whenever priests start making up rules, they often become tempted to regulate every detail of people's lives. When less enlightened laws and values become entrenched in religious scripture, they become very difficult to change without abandoning the whole tradition.