What reasons do Christians have to believe there is one God? Related to What reasons does Christianity give for &quot;Why There Must Be A God?&quot;.

In my reading on apologetics, I have come across many arguments for Theism, but next to nothing for Monotheism. I've read the phrase, "the chaos of polytheism," without a more rational argument, though I firmly believe that one exists.

What arguments exist for Monotheism vs. other Theisms?
A common argument for theism is the Cosmological argument - that there must have been a first cause for the universe. Christians believe that everything that exists is the result of God, who is uncreated and self-existent.

If the universe has a single cause then it follows its existence is the result of a single self-existent being. Could there somehow be multiple self-existent beings? Well yes, but to be a single cause for the universe those beings must be in such a great unity. This could be argued to be the case for the Christian view of God, the Trinity, who is three persons in one being.

In many (perhaps most) polytheistic religions most of the gods were actually created from the original creator god. In my mind those gods don't deserve to be called gods - call them spirits instead.