Locutus/KJV1611, Can I add to this? Not to take anything away from my new friend, Locutus, who I am really starting to get a huge man crush on (don't worry, I'm straight and married), but this idea of "drying up the Euphrates" preparing the way for the enemy has both literal and spiritual OT significance.
In historic times and really today, a river, sea, or even a brook provides a natural defense. We have two examples of God divinely intervening to dry up a body of water for the assistance of His people, the Red Sea and the Jordan (Josh 2:10, 4:23). So, why can't God do the same thing to aid an army He is sending against His (soon-to-be former) people?
We also have an example of a severe drought drying up the Euphrates before and this happened specifically in relation to Babylon's destruction (Another fortified and seemingly impenetrable city, which Jerusalem is being compared to BTW) as mentioned in Jer 50:38:
A drought is against her waters, and they will be dried up. For it is the land of carved images, And they are insane with their idols.
When waters are dried up, the natural defenses are gone as we see here from John's favorite passage to steal imagery from, Isa 37:35:
I have dug and drunk water, And with the soles of my feet I have dried up All the brooks of defense.’
Now, we know there was a severe famine in the Land prior to the War and famines are often caused by droughts. This is mentioned in the "beginnings of sorrows." So take your pick, the waters of the Euphrates were either "dried up" (lowered, making it easier to cross) by drought or done divinely by God. I'm leaning towards the first, less fantastic, explanation. Regardless, Titus' troops came from that area and that's not in dispute and Locutus and I have given KJV1611 reasonable Biblical arguments for the fulfillment of this miracle.