(Taken from Chapter 10 of Steve Wohlberg's book, Exploding the Israel Deception)
"The sixth angel poured out his vial upon the great river Euphrates; and the water was dried up, that the way of the kings of the east might be prepared." Revelation 16:12. In order to correctly understand this prophecy, we must first study some ancient Bible history about Israel and Babylon. In 605 B.C., "Nebuchadnezzar king of Babylon" came "unto Jerusalem, and besieged it." Daniel 1:1. Jerusalem was conquered and Israel was taken captive for 70 years (Daniel 9:2). After those 70 years, an amazing set of circumstances occurred. The Euphrates was dried up, Babylon was conquered from the east, and Israel was delivered. As we shall soon see, this history forms the background for a true understanding of Revelation 16:12.
Ancient Babylon sat on the river Euphrates (Jeremiah 51:63, 64). A wall surrounded the city. The river Euphrates ran through Babylon, entering and exiting through two spiked gates whose bars reached down to the riverbed. When these double doors were shut and all other entrances were closed, Babylon was impregnable. Ancient Babylon was "most proud," "a golden cup…that made all the earth drunken…of her wine." Jeremiah 50:32; 51:7. Yet she was to fall suddenly and be destroyed (Jeremiah 51:8). Then God would call Israel, saying, "My people, go ye out of the midst of her." Jeremiah 51:45. As we shall soon see, these exact words are repeated in the book of Revelation to spiritual Israel about the importance of coming out of modern Babylon (Revelation 17:4, 5; 18:2-8).
In 538 B.C., on the night of ancient Babylon’s fall, her king and subjects were drunk with wine (Daniel chapter 5). So were the guards, and they forgot to fully close the double doors. Over 100 years earlier, God had predicted concerning Babylon and the Euphrates, "I will dry up thy rivers." Isaiah 44:27. The Lord also spoke about "Cyrus," who conquered Babylon, saying, "I will…open before him the two leaved gates; and the gates shall not be shut." Isaiah 45:1. Moreover God called Cyrus "my shepherd" and "his anointed" (Isaiah 44:28; 45:1). Thus Cyrus was a type of Jesus Christ. And he came "from the east" Isaiah 46:11!
Inside the British Museum in London lies the famous Cyrus Cylinder. It describes how Cyrus, a general of Darius, conquered Babylon. Cyrus and his army dug trenches upstream alongside of the river Euphrates. By diverting the water, the river gradually went down as it ran through the city of Babylon. No one noticed. At night, at the height of Belshazzar’s drunken feast, the water became low enough for Cyrus and his men to quietly slip under the double doors, which had been left open. Quickly they overran the doomed city, killed the king (Daniel 5:30), and conquered Babylon. Then Cyrus issued a decree to let Israel go (Ezra chapter 1).
[The curious reader may see more at http://www.endtimeinsights.com/bookchaptereuphrates.html, "When The River Euphrates Runs Dry"]
Cyrus, God's Annointed Shepherd provides a more detailed description.(also here.)