Here is a preliminary list of some of the playable countries. I will, in due time, set various ratings and levels for the different countries to reflect their populations, productivity, military power and so on:
Minor nations of the NW:
Suel Barbarians (Snow-, Ice- and Frost-barbarians and Ratik.) The Bone March (Mostly Orcs). The Theocracy of the Pale (Human). The tribes of the Griff Mountains and Raker Mountains (Humanoids and monsters of many kinds. The tribes of the Timberway Forest (Elves, Fey, Humanoids and Monsters of many kinds). Gamboge Forest (the same) The Troll Fens (Mostly Trolls). Phostwood (Tenha partisans, Undead, various Monsters). Fellreev Forest (anti-Iuz partisans, various Monsters)
The Great Kingdom:
(Mostly Humans)
(Northern Aerdy, United Kingdom of Ahlissa, Almor, Rel Astra, the Sea Barons.)
Minor nations of the SE:
Irongate (Dwarven, major city). Iron Hills (Dwarven). Sunndi (Human). Lendore Isles (Elven). Grandwood Forest (Elven, Fey, Human).
Scarlet Brotherhood:
(Suel Humans, Monsters.)
(Tilvanot Peninsula, Lordship of the Isles, The coast of Hepmonaland, Onwall, Idee, The Olman Islands, The coast of the Amedio Jungle, The Hold of The Sea Princes.
Greater Nyrond:
(Mostly Human)
(Nyrond, Almor, Flinty Hills (Dwarves, Gnomes), The Celadon Forest (Elves, Fey), The Duchy of Urnst, The County of Urnst.
Empire of Iuz:
(Undead, Goblinoid, Orc, Human, Demon)
Stonehold, The Empire of Iuz, Tenh, The Bandit Kingdoms.
The Kevellond League:
(Human, Halfling, Gnome, Elf, Dwarf)
The Shieldlands, The Kingdom of Furyondy, Veluna, Verbobonc, Dyvers, Bissel Gran March, the Kingdom of Keoland.
The Domain of Greyhawk*:
(Greyhawk (metropolis), Hardby, Cairn Hills, Gnarley Forest).
*Power behind the Throne: Eluvan.
The Empire of the Pomarj:
(Orc)
Celene:
(Elven)
The Lortmil Confederacy:
(The most powerful dwarven nation)
The Lortmil Mountains (Dwarf), The Lortmil Underdark (Dwarf), The Kron Hills (Gnome), The Lorridges (Human, Gnome, Dwarf), The Duchy of Ulek (Human, Dwarf), the County of Ulek (Human, Dwarf), The Principality of Ulek (Human, Dwarf).
Minor Nations and Regions of the SW:
Dreadwood (Monsters, Goblinoids). The Yeomanry (Human). Sterich (Human). Geoff (Humans under Giant rule). The Crystalmists Mountains (Humanoids, Giants, Monsters) The Crystalmists Underdark (Drow). The Joten Mountains (Giants). The Hellfurnaces (Humanoid, Gaints, Monsters). The Hellfurnaces Underdark (Drow, Formians). The Valley of the Mage (Powerful Wizard and his slaves).
Minor Nations and Regions of the NW:
Ket (Bakluni Humans), The Yatil Mountains (Giants, Dragons, Humanoids, Monsters). Tusman Hills (Bakluni Humans). Highfolk (Elves). Vesve Forest (Elves, Treants, Fey, Monsters). Perrenland (Human). Wolf Nomads (Human). Tiger Nomads (Human). Burneal Forest (Quaggoth, Monsters). Cold Marshes (Undead). Blackmoor (Undead, Human). Land of Black Ice (Unknown)
The Bakluni Empire:
(Bakluni Humans)
(The Zultanate of Zeif, The Caliphate of Ekbir, Tusmit, Udgru Forest, The Plains of the Paynims, Ull.
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The Nations of the West:
Skip Williams said:
Barbarian Seameast: A windswept land covered with primeval forests where fiery but convivial tribesmen dwell.
Celestial Imperium: A vast nation peopled with a hard-working peasantry ruled by a complex bureaucracy.
Dragons Island: Tales from the Celestial Imperium speak of a land ruled by a dragon prince. If such a place exists, it probably lies here.
Elvanian Forest: An enclave of lofty trees clinging to foothills rising from the desert below. Elves and other wild sylvan races dwell here.
Elven Lands: It seems that eleven seafarers crossed to (the? RH) Solnor Ocean millennia ago and established a kingdom upon this peninsula.
Empire of Lynn: A sea of burning sands fill most of Oerik's western end. The fabled city of Lynn, perhaps settled by seafarers from the Flanaess, has grown rich from coastal trade and the desert's mineral wealth.
Erypt: An arid land ruled by a dynasty of priest kings.
Fireland: A land not unlike the Hellfurnaces region of the Flanaess. Volcanoes and geysers sprout amid glaciers. A hardy folk dwells among the coastal fjords.
Gigantea: A land populated by giants, or so I've heard tell.
High Khanate: An and land peopled by two tribes of sturdy nomads. The inlanders resemble the horsemen of the Balkanish (Baklunish? RH) Basin, but on the coast they take to boats.
Hyperboria: My own name for an icy continent whose interior holds Oerth's north pole and secrets even I have not fathomed. A semi-permanent bridge of ice connects the land to Oerik proper, but the crossing is treacherous at best.
lshtarland: A land watered by southern storms and at least two great rivers. The city of Ishtar vies with the merchants of Lynn and the warlords of Tharquish for control of coastal trade.
Kingdoms of the Marches: A temperate land filled with princely states. Perhaps another locale colonized by seafarers from across the Solnor.
Low Khanate: A companion realm to the High Khanate; named more for its location in a deep vale below the mountains than for any inferior status. A hidden valley reputedly contains the tombs of khans from both realms.
Nippon: A densely populated island nation of fishermen, warriors, and poets. Unsure of the place's real name.
Nippon Dominion: A protectorate only recently conquered by the warriors of Nippon.
Orcreich: A nation of orcs ruled by a tyrannical king. The orcs seem to thrive under the brutal regime.
Polaria: Not a land mass at all, but a collection of islands locked in a semi-permanent ice cap.
Red Kingdom: This land is so named for the color of its rocks. It's inhabitants remain unknown to me.
Suel Empire: You know this area as the Sea of Dust. Tales of its former glory is known to you.
Tarquis Dominions: An ancient protectorate of the Tharquish Empire.
Tharquish Empire: An island nation of seafarers who have ambitions that extend to the neighboring continents.
The Tribes of Enllaves: A land of proud desert nomads who eke out a living on a high plateau that escapes the worst heat of the sand sea. A few tribes-men live in mud-brick towns built around central squares that contain steep-sided pyramids. I have never learned whether the pyramids serve as monuments, tombs, temples, or something else altogether.
Wall of Tsian: A massive fortification separating the Celestial Imperium from Orcreich, a formidable deterrent to anyone but the king of Orcreich. The Imperium has begun another, even grander wall farther west.
Zindia: A tropical land where rich cities rise from steaming jungles.
Celestial Sea: A warm shallow gulf where merchants from Erypt and the Imperium ply their trades.
Gulf of Ishtar: The privateers of Tharquish and the fleets of Ishtar vie for control here.
Gulf of Ra: A deep body reputed to hide a kingdom of sahuagin.
Jothunheim Sea: A frigid body of water littered with icebergs. Giants ply the waters in great drakkars.
Mare Mysticum: A mystery to me.
Ocean of Storms: A region of gray sea lashed by endless tempests.
Oceanum Titanicum: The eastern-most extent of what you know as the Solnor ocean.
Pearl Sea: So named for the rich pearl beds found on Nippon's eastern shores.
Sea of Hyperboria: An ice-choked stretch of deep water where the coastal tribesmen of the High Khanate hunt and fish from hide boats.
Sea of Nippon: A body of water made infamous by freak storms and enormous sea monsters - if the tales prove true.
Sea of the Dragon King: A deep arm of the pearl sea noted for its cobalt blue waters and teeming coral reefs.
Sea of Thunder: A smaller, but no less violent, companion to the Sea of Storms.
Organizations not primarily based on a specific location:
The Circle of Eight:
(A powerful group of Neutral high level Wizards)
The Black Brotherhood:
(An undercover organization inflitrating the Scarlet Brotherhood, seeking to bring about an apocalypse)
Various Churches:
(Though they have lost all their spellcasting-ability many clergies still hold considerable power over the peoples of Oerth)