I've never really studied the question and this thread ought to be interesting. For starters, here's the Wikipedia article on Early Monotheism:
The religions that are monotheistic today are often thought of as having been of relatively recent historical origin although efforts at comparison are usually beset by claims of most religions to being very ancient or eternal. Eastern religions, especially in
China and
India, that have concepts of
panentheism, are notably difficult to classify along
Western notions of monotheism vs.
polytheism. Attempting to compare the two is much like asking how many sides a circle has when comparing to a square, in that it makes no sense.
The earliest examples of monotheism include two
Rigvedic (1500 - 1200 BCE) hymns (10.129,130) to a
Panentheistic creator God; the
Shri Rudram, a
Vedic hymn to
Rudra, an earlier aspect of Hinduism's Shiva often referred to by the ancient Brahmans as Stiva, a masculine fertility god, expressed
monistic theism, and is still chanted today; the
Zoroastrian Ahuramazda and Chinese
Shang Ti.
In the
Ancient Orient, many cities had their own local god, though this henotheistic worship of a single god did not imply denial of the existence of other gods. The
Hebrew Ark of the Covenant is supposed (by some scholars) to have adapted this practice to a
nomadic lifestyle, paving their way for a singular God. Yet, many scholars now believe that it may have been the Zoroastrian religion of the
Persian Empire that was the first monotheistic religion, and the Jews were influenced by such notions (this controversy is still in debate)
[2].
The iconoclastic cult of the Egyptian solar god
Aten was promoted by the
pharaoh Akhenaten (Amenophis IV), who ruled between 1358 and 1340 BC. The Aten cult is often cited as the earliest known example of monotheism, and is sometimes claimed to have been a formative influence on early Judaism, due to the presence of Hebrew slaves in Egypt. But even though
Akhenaten's
hymn to Aten offers strong evidence that Akhenaten considered Aten to be the sole, omnipotent creator, Akhenaten's program to enforce this monotheistic world-view ended with his death; the worship of other gods beside Aten never ceased outside his court, and the older polytheistic cults soon regained precedence.
The worship of polytheistic gods, on the other hand, is seen by many to predate monotheism, reaching back as far as the
Paleolithic. Today, monotheistic religions are dominant, though other systems of belief still exist.
