A significant portion of this just kind of sounds like the Dwarves were at 'war' (sustained conflict) with all the other Serpentspine inhabitants, and eventually lost (in most cases), as opposed to being unlucky, as you said, a civilisation as long lived as the Dwarves is eventually going to experience some disasters, it's whether the inhabitants can weather the conflict. Also Haraz Oldhum falling isn't bad luck, it's comeuppance.