Wouldn't a race which has horns suffer from a distinct disadvantage on the battlefield due to being unable to properly wear a helmet? I'm guessing that with enough engineering you could build a helmet around the horns, but I can't imagine a way it would be nearly as sturdy as any human one. Maybe you could defend the face and the neck, but the top and likely back of the head would be completely exposed. It'd be suicide to go to war like that.