How does the Euphrates divide religions east and west?

Les explains that the Euphrates River is the great boundary between east and west, and has always been the major obstacle for those traveling from the east to the west. Religiously, he says the same division holds: east of the Euphrates has always been predominantly pagan idolatrous religions, while west of the Euphrates are Judaism, Muhammadism, and Christianity. He notes Muhammadism is not akin to the pagan idolatrous religions of the east. Earlier he also ties all pagan mythological religions back to the Tower of Babel on the Euphrates, where he believes four powerful demonic beings were bound.