beyond the wide world's end

Probably the only relevant bit is that Cas's claim to the throne is she's a direct descendant of the previous king and Miraz is only the previous king's brother, Miraz's claim to the throne is he's a close male relative of the previous king and Cas is only a female, and if we throw in a few more generations and confuse matters a bit, that's the Yorks and the Lancasters.