Pretty good job
I liked it. The guitar was good, but it would be even better if you made the guitar play a wider range of notes rather than a single note per measure. A nice powerful snare drum would have been a good accompaniment as well.
Another thing, I don't really see this as a "soldier's song". In my opinion, its too happy, where in a soldier song it would be more dark and brooding. But hey, it seems like you have a good start. After all, this is just a demo. Just look for more variation in your final product.
Oh yeah, and check out my newest song "Futureform".