This isn't really based on very much, but what do you think of the myth world sort of based on the Europe and Byzantine empire area? Although the maps aren't very similar, there was the city of Tyre somewhere in the lands conquered during the first crusade, obviously similar to Tyr from Myth. Tyre is obviously in the wrong place, but... bear with me here. The reason I said Byzantine empire area, though, was because that was the closest thing I could think of to the Cath Bruig Empire... after all both were conquered at one point or another, and both were centers of high culture and they both had excellent militaries. The reason Constantinople fell was because their enemies had what must have seemed like infinite forces at their diposal, and the same holds true for Muirthemne. And both western europe and the free cities of the west made semi-desparate attempts to recapture these fallen cities, Europe at the command of the Pope, who was the closest thing to an overking of Europe, while the people of the free cities went to retake Muirthemne at the command of Alric, who was the overking of the west. Although europe failed to restore Byzantium, if they had had mortars cannons, well...
Both Europe and the west had at least part of their land conquered by their respective enemies at the time. And both the Muslims and Balor came out of the east (admittedly, northeast for Balor and southeast for the Muslims...)
The Heron Gaurd were elite forces, while the Europeans and Byzantines had their holy knights (such as the Templars, for example).
So basically the set up would have been like this -
The West <-> Europe
Balor and the Undead Horde <-> Muslims (not to offend anybody of that faith. I'm not saying they were evil, just the enemies of the west)
The Cath Bruig Empire <-> Byzantium
Muirthemne <-> Constantinople
Tyr <-> Tyre (though obviously in the wrong place)
If anyone can give me a parallel for the Drowned Kingdom of Yer-Ks, please do.
So? How messed up is my theory?
P.S. - Does MHR stand for Myth Historical Reference?