Monotheism results in a very focused society, with absolute values and unquestioning support – until a flaw appears, opposition appears, and war breaks out. Monotheism is inherently hostile to democracy and free choice.
It is easier to manage a theocracy for a population that is ethnically and culturally homogenous. The wider it grows, the more allowances have to be made, and the faster the monotheism erodes. The most effective monotheisms are cults operating in isolated compounds.
Polytheism allows the possibility of behaving in different ways, each way being appropriate for a different god. Those who want to worship Venus are not forced to live by the standards of those who worship Mars.
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