The underlying principle of monotheism follows from such simple logic that even polytheists generally accept it. Call God the Supreme Being, the Unmoved Mover, or any other similar concept, the basic idea is still there: If you accept any divinity, then either there is an Ultimate Cause of Everything, or you have infinite regression (turtles all the way down, so to speak). Once you get to the concept of an Ultimate Cause, someone will see fit to worship that Cause. After all, if you believe in many gods, and One Cause to Everything, including those gods, then that Cause is higher than the gods, and is, at minimum, deserving of equal worship as the gods themselves. And, as Aquinas says, and This, all Men call God.
Then, of course, you have the general acceptance throughout all Indo-European societies of a Supreme god, Dyeus (Deus, Zeus, Tiwas, Iupiter, etc. etc.) that even the pantheon worshipped across most of Eurasia is structured to point towards one God, even obliquely.
To avoid Monotheism, you'd pretty much have to avoid any theism. Which is... well, I have to think its impossible.