I have a rather, opposite view of the factions, perhaps from my many years of playing World of Warcraft and shouting/typing "For The Horde".
Crownies: The seemingly dominant faction. The Crownies run the city guard across all the lands and have ties with royal bloodlines. The average crownie is honourable, but as you ascend the ranks you get a real look at the Crownie faction. The top ranks are full of fanatical egomaniacs who are constantly playing a game of intrigue and assassination in order to best their superiors. And in doing so, they have no regrets against manipulating the peasants and their soldiers. Despite the in-warring, these men have worked together to expand their empire across the continent (i.e. think all of Europe, Asia and Africa).
The Mage Towers: An order of magic-users that have congealed together to give them influential weight. In each city and trade hub, this order has constructed an identical tower to the original. The good/evil side of the faction changes from mage to mage. Known memebers include, but are not limited to, priests, wizards, witches, necromancers, sorcerors and druids. An important thing of note is that all magical and scientific institutions are funded by them.
The Dwarves: These short but stout people have recently arrived of the surface after fleeing their single, fortified city. The cause of their flight was an earth elemental summoning gone wrong. Thousands upon thousands of elementals exitted the rift before it timed out. Now with no home, the Dwarves have contracted themselves to the Crownies, cutting open new mines and relying on force to ensure they are not scammed. It is impportant to be aware that while Dwarves may be a minority, they have vast control of the economics of the Crownie lands.
The Rangers: A group of mercenaries who specialize in ranged combat. In each city or trade hub, a local tree is cultivated and transformed through druidic powers into treehouses. They can be hired by anyone for the right price.
The Orcs: The native inhabitants of the mountain ranges, the shamanistic orcs had been living peacefully before the Crownies arrived. Seeing a force of labour and war more powerful per capita than their own, the Crownies attempted to use superior tactics and technology to enslave them. The orcs reactions were less than happy. They called upon their allies: the Trolls, and Beast People (i.e. Giant Trolls, and Adventurer monsters/wookies/minifig piraka/gamoreans). The orcs also began shifting a war culture, using the massive mountains beasts as weapon rather than labour. The orcs and their allies quickly formed under one banner and have been ferociously raiding the Crownies off for years, while attempting to spare innocents. Recently they have sworn allegiancy to the Black Knight Vesz'aste.
The Undead: The usurpers of the Crownie civilians. When a revolt break out in Crownie lands, the Crownieleaders put it down with force. By hiring priests, the Crownies have the rebellion leaders stripped of flesh and blood, left to wander as skeletons the rest of their lives. These skeletons are not powerless, as the retain all skills they had while living, as well as their minds and souls. They too have sworn to Vesz'aste, and in return have been taught how to use magic in a way that lets them fight as if they were in full armour, not just dusty old bones.
The Black Knights: Not the Lego faction of the Black Kinghts. These soldiers are from islands south of the Crownie empire. Under the command of Black Knight Vesz'aste, they have mixed demons into their heritage, sa well as employing them for field use. The goal of the Black Knights is to cut a swath in to Crownie coast, and potentially into the mainland. Only small outposts lie in large cities, otherwise they rely on Undead and Orcish settlements for campaigns.
Bandits: The general term given to any small group of people against the Crownie forces. Similar to the Rangers, bandits will help those who stand against the Crownies for a price. They also offer inland bases for Shipfolk.
Shipfolk: These peple live their whole lives on ships or in water, they only set foot on land when building new boats. And speaking of boats, the Shipfolk are the only ones who know the trade, going so far as to kill traitors and kidnap others who are close to finding out. They have an archeopelago on the other side of the world, surrounded by a ring of islands with a single passage out.
These are my factions. They may seem large, but in reality they are rather small, with the only settlements I have being a port, a town and an orc camp (aside from the boats). I hope to build upon them soon, maybe the next Castle line (read: after Crownies) will have some promising factions.