Monotheism is Older Than Polytheism
The book "The Golden Bough," by James Frazier (1912) promoted the now disproved idea that religion evolved from primitive animism, to polytheism, to henotheism and then to monotheism.
W. Schmidt proposed that monotheism is older than polytheism. He sees animism, polytheism and henotheism as later corruption. (Origin and Growth; Primitive Revelation).
The leading Bible archaeologist of America William F. Albright commented: "There can no longer be any doubt that Fr. Schmidt has successfully disproved the simple evolutionary progression...fetishism--polytheism---monotheism, or Tyler's animism--polytheism--monotheism....The simple fact is that religious phenomena are so complex in origin and so fluid in nature that over-simplification is more misleading in the field of religion than perhaps anywhere else." (From the Stone Age to Christianity, p. 171).
John Mbiti said that in primitive religions there is still a widespread concept of high god or sky god. He remarks: "in all these societies, without a single exception, people have a notion of God as the Supreme Being. (see Mbiti, African Religions and Philosophy).
Egyptologist and Old Testament scholar K.A, Kitchen writes..."monotheism was not invented among uprooted Jews during the Babylonian exile in the sixth century B.C. It was clearly proclaimed by Akhenaten in Egypt in the fourteenth century, and he was not a contemporary of Nebuchadrezzar II of Babylon in the sixth century! On this matter, old-style nineteenth-century biblicist dogma of the evolution of religion must finally be abandoned, on strictly academic grounds -- especially as such belief had roots earlier, and had echos in Egyptian religious thinking and writing into the thirteenth century (p. 396). Also, in twelfth -- century Babylon Marduk attained a monotheist role for a time." (K.A. Kithchen, "On the Reliability of the Old Testament," pp. 395-396).
(Kitchen is a British Bible scholar, Ancient Near Eastern historian, and Personal and Brunner Professor Emeritus of Egyptology and Honorary Research Fellow at the School of Archaeology).
The Book of Job (Old Testament) is pre-mosaic, and also teaches monotheism.
The Ebla tablets furnish archaeological evidence for ancient monotheism.
Monotheism is a better explanation than polytheism pursuant to Occam's Razor, since it is more simple.
Theophilus of Antioch (2nd century) wrote three books that attack pagan idolatry. (see To Autolycus).
Athenagoras (2nd century) wrote against paganism and idolatry. (see Apology).
Augustine wrote against paganism. (see The City of God, Books 1-10).