I honestly liked this piece. There were a couple of misspelled words and some grammar that threw me off in a couple of places, but as prologues go I thought it was excellent.
I don't think your explanation of the magic was bad at all. I like how you got to show the powers of the boy, and then had Dezrius think about each one. It gives us just a little bit of action and keeps it from being an info dump. I also think it wasn't very hard to catch on to what a Geas is, so good job there.
The one question I had is about the last paragraph. I read all the submissions on my Kindle, since it makes it seem more like a book to me, and that part stood out, and not necessarily in a good way. I guess you could say that I thought it was a little heavy handed. Now, you don't have to change a thing, but if I had written it, it might have said something like
"...his teachers would see him graduate a military man, straight as an arrow and full of imperial fervor. Perhaps it was just the Geas, but obedience seemed to fit the child quite well, Dezrius thought. He was rarely wrong about these things."
Something that doesn't just give us the fact that everything's gone to hell. I guess the last paragraph was just a little jarring, since it moved us forward thirteen years in one sentence, and we really don't know the story of what happened in that time at all.
So yeah, I would have preferred a milder ending to the chapter, but everything else flowed very well. And this is coming from a guy that doesn't really like Prologues.
A few notes: do a ctrl+f for Girshka, since I noticed you had it spelled GRishka most of the way through, but a few of these showed up. Also, there's still a commejj in there somewhere, so you might want to switch that out. I was okay reading it, it didn't jar me too much, but I suppose some others might find the double j annoying.
Great stuff.
P.S. I try not to ever delete an email, so I've combined everything you've put up so far and converted it for the Kindle. I'll be reading it this week, and I'll try to get you feedback on every chapter.