- The Empire of Thyatis -- should be included because it is one of the major powers of the Known World of Mystara and therefore, certainly a major power in Enigmundia) and because it is the empire that Karameikos is associated with. Thyatis has a distinctly Roman-inspired culture that is somewhat at odds with the more Byzantine-attired folks of Karameikos. It is characterized as being primarily utilitarian (hence their view of weapons and magic being of equal value in strategy and tactics) and conquest-driven in nature (kept in check only by their rival to expansion, the Empire of Alphatia).
After seeing the portrayal of Roman attitudes toward slaves and gladiators in TV shows like Rome and Spartacus, I'm favoring the reason for the monotheistic state religion's popularity as the belief in the equality of all humans, and the need to treat one another with respect, kindness, etc -- overwhelming support in the non-citizen classes of society plus some support higher up propelled it to its current status. At the current time, the monotheistic state religion practices religious tolerance but the officials and social climbers of the empire would do well to shed their pagan ways and worship the one true god.
- The Empire of Alphatia -- should be included as the only other major power of the Known World. It is ruled by mages, and is characterized by a chaotic view of life.
Honestly, I never really understood how a society mages could possibly withstand the assault of the Thyatian Empire when both sides use magic and the Alphatian chaotic nature would therefore sabotage many key elements of military strategy such as logistics and planning. This element of the Alphatian Empire would have to be drastically retooled.
I'd actually want to play with the idea that my version of Alphatia is fragmented from the original Roman-esque mega-empire that Thyatia came from. Unlike Thyatia, however, the monotheistic state religion didn't take root and various pagan religions still exist (most of those surviving tend to veer toward religious portfolios that encourage the pursuit of knowledge in the arcane).
- The Principalities of Glantri -- should be included because one of the Immortals lives there, and he's the same one that's mentioned in module X2 -- Chateau d'Amberville (Castle Amber)! Still, with its all magic, no cleric stance it begs the question: does it have anything to do with Alphatia?
Since I'm pulling the 'splintered empire' bit already with Thyatia and Alphatia, I could have mages from Alphatia and / or Thyatia settle in this magic-rich environment and share some of their 'modern' political views.
But I'm also fond of the idea of having very ancient mystical orders based in this one country that is out of the reach of the so-called Empires. They could fund expeditions to ancient mystical sites all over the world, they could be behind the latest in magical research, and they could be secretly pulling the strings of various mystical fraternal brotherhoods (because these mages tend to invest in longevity, and those are just the living mages).
Yes, Glantri could be a hidden or at least distant power that the Empires are aware of because its existence predates their own origins. And the ancient texts have hidden messages that may give them good reason to fear Glantri.