The Flavour

Or the fluff, as some like to call it. Mighty Empires is intended to be used in the Warhammer Fantasy setting, but since I am not using WFB to resolve battles there is no particular reason to stick to that. It also does not fit particularly well with the game itself; dwarves having overland empires, wood elves having extensive empires at all, and orcs having stable empires at all would be odd for that setting. Though, of course, there are few fantasy settings where this would make sense I guess.

I decided to use the Eberron setting from D&D instead. Eberron works better for this sort of game I think, because it has few clearly good or evil factions: instead most races in Eberron have no intrinsic alignment and most are capable of having stable civilisations. An alliance between orcs and humans is plausible in Eberron where it would not be in Faerun or Warhammer. And ME campaigns with players usually have all sorts of temporary alliances happen.

So, let's see who the contestants are.

Sulatar

40,000 years ago, a giantish empire controlled the continent of Xen'Drik, and all elves lived as slaves of the giants. A great war with the dragons shattered the empire, and the elves revolted to escape from slavery. The Sulatar were the elves that remained loyal to their masters. But the Giant civilisation collapsed and the giants mostly regressed to a primitive state, leaving the Sulatar to stand for themselves. The Sulatar believe in no deity but worship elemental fire, as many of the Giants did before them. They claim what they consider their inheritance: the continent of Xen'Drik and its ruined Giantish settlements.

The Sulatar are hated by other elves for their loyalty to the Giants, are shunned as heretics by followers of the Sovereign Host and the Dark Six alike (which is most of the population of Eberron), and are local enemies to every tribe or group in Xen'Drik. As a consequence the Sulatar have a strong martial tradition, with more warriors than hunters. They fight with sword, spear and bow, and their wizards and clerics specialise in fire magic.

The largest settlement in Xen'Drik is the Sulatar's Obsidian City; that is a long way  to the South of where the campaign will be fought though.

The Storm Lords (Human)

Xen'Drik has only one large human settlement, the city of Stormreach. The city serves as a hub for intercontinental trade on Eberron. It is a former Giantish city, huge in scale, the ruins of the old walls towering over the comparatively humble dwellings of most of the settlers within. The city is the most prosperous in Xen'Drik though, and is the second most populous on the continent.

The city is ruled by the Storm Lords. They are the nobility of Stormreach, though that means little more than that they are the descendants of the wealthiest and most powerful of  the original smuggling and pirate interests that took up in this area. They maintain a reasonably stable and fair government in the city, provided they receive a sufficient cut of the trade passing through. The Storm Lords maintain a standing army; for military operations, however, they would turn to House Deneith for additional mercenary troops, often shipped over from Khorvaire.

The city itself attracts adventurers, criminals, traders, and refugees from the Last War looking for a new life. It is very diverse, with only around half the population being human; there is a large gnomish population as well, and elves, dwarves, halflings and half-orcs are all common enough. The rulers are largely human though.

Hammerhead Clan (Duergar)

Sometimes called grey dwarves, Duergar are an unusual Eberron faction in that they are considered evil. However this seems to stem largely from their greed and ruthlessness. They are hardy fighters and miners.

White Fang Tribe (Orcs & Goblins)

Goblinoids are common in many parts of Eberron, and the power vacuum left by the fall of the Giants has allowed many tribes to establish a foothold in Xen'Drik. The White Fang tribe is a typical goblinoid mix: orcs in charge, goblins in subservience, worgs as pets and the occasional troll.

(not my mini, just throwing in an image for flavour)

Xen'Drik

The interior of Xen'Drik is sparsely populated. There are tribes of hobgoblins, remnants of the former Dhakaani empire; orc tribes; tribes of primitive giants; Umbargen and Vulkoorim Drow tribes; human settlements. The continent is also scattered with ruins of Giantish temples, cities and burial sites — often abandoned but sometimes settled.