I'm going to go off what I think the previous message said and form a theory. I don't see much support for this, but I haven't seen anything to contracdict it.
In the last cycle, the Cath Bruig ruled what is now the province and probably all the other human and dwarven lands as well. (This is supported fairly well by Myth 2.)
Maybe the 20 years war was fought between the eastern and western section of the Cath Bruig, and led to it's break-up, which is how the dark were able to over-run Muirthemne.
Note that the fall of Muirthemne happens during the twenty-years war.
