I'm not OP, but my understanding is that it's the Helvan Empire, and so the Helvan Army, and then the people are Helvans. Similarly to how the Ottoman Empire had the Ottoman Army and the people were Ottomans. I think Helvenand is just the name for the geographical region itself?
I apologize if I've misunderstood, there's a lot of information here (which is a good thing!!). ^-^""