Gaming in the World of Edyleine

The World of Edyleine is intended to be a versatile game setting that could be played with any game system that supports robust magic. Most nations of any significance are intended to be durable to a point of about fifteenth level or so, meaning that a party has to be about that level in order to break that country, and even then they may have to deal with more durable neighbors. Epic level play is possible from dealing with the major players, though epic level wilderness exists as well in areas like the Blistered Lands and The Land Beyond Mankind.
There are a number of NPC's of level 20 (In D20 terms) and higher, for several reasons. 1.) Most kingdoms have some familiarity with rampaging epic level characters and don't want that to happen to them. 2.) If the PC's are the only epic level folks around and the new dude rolls up a 25th level somethingoranother, where did he come from?