[tinkthank]

I think the original poster has "Warcraft III" in mind, the "War Machine (Catapult with flaming rocks)" being the hint for me.
For those who don't know it, Blizzard made a very believable nation of proud, tundra-crossing shamen and proud, strong warriors which are somehow reminiscent of a cross between "native american" "Indians" and Mongolian hordes (WIII
orcs refer to themselves as "The Horde").
So for this reason, Blitz, the majority here is not going to understand your feel for this nation, since the majority here dislikes WarcraftIII or has never played it. (I thought it was an excellent and well-crafted game, I just dont like RTSs.)

- I like your point with a siege engine. Could be tough to do. It would be a lifeless construct capital-only requiring huge resources and a siege bonus like the Ulmian engineer.

- I think fire and blood should be strongish paths, with perhaps some foreign death and earth.

- some form of berserking should be in for one type of troop, perhaps coupled with this idea: Those units that go berserk have a chance of entering a state of blind rage, where they simply attack the nearest unit for a certain amount of time (I think the spell is called: "Rage"?); this could be a sort of berserker that fits into the theme. Or perhaps they have the "Gone Berserk" (a la wolf pelt) attribute always on?

Just some thoughts.
Good luck!