New Defender's Study Bible Notes
9:14 Euphrates. These four angels are also Satanic angels, for they have been “bound” because of past sin. They have not, like the previous group, been bound in the bottomless pit, but “in the great river Euphrates,” so apparently their particular sin was at a different time and place. Perhaps this particular horde of fallen angels, with their four captains, had been associated with the first great human rebellion after the Flood, when Nimrod led mankind to rebel against God at Babel, located on the Euphrates. As a result, God had scattered the people around the world, confusing their tongues (Genesis 11:9).
The invisible host of heaven, however, who had instigated this rebellion and whom Nimrod had sought to worship in his great temple tower built “unto heaven” (Genesis 11:4)—that is, with a shrine dedicated to the host of heaven, the angels and their starry realms—had not been scattered. Rather, they were confined to the Euphrates where they had established their base. This, of course, is not stated in Scripture, but seems a plausible explanation of why Babylon and its environs (including Baghdad, which has been more prominent than Babylon during the church age, as a center of the Islamic rebellion against Christ), seems ever since to have been the greatest enemy of God and His people.