UPDATE 12/24/14 - updated the various factions. Fixed Council of Undying, added Cataclysm Society.
The Golden Empire of Tannishpopulation: 3 million (70% human, 20% half-human, 10% other)
Current leader: Basle Tarnis (17th Emperor since Empire's creation)
Tech status: heavily industrialized
Magic status: strictly controlled
The Empire used to be viewed as what humanity could achieve with hard work and perseverance. But since Emperor Basle took the the throne 10 years ago, the whole country has fallen into decay. His demand for power has brought ruin to the Empire. Only 5 years ago did he declare war upon the elves and began his invasion. Some progress has been made, but the Imperial Legion has been pushed back more times than they'd care to admit.
Industralization started about 25 years ago, and while the Dwarves have the jump on them, the humans are quickly becoming the strongest in steam-tech. Advances in firearms have been lead by the humans, and they are only second to the Dwarves in Steam Knight tech (the Dwarves do tend to keep the best stuff for themselves...)
Astetics: The Empire has a WW1 German fashion to them. However, weaponry has a industralized version of the Roman Empire (IE: gladius, sword and gun legions, etc). Artechure also follows this style.
The Altza Kingdom
Population: 1.5 million (75% elves, 15% half-elves, 5% humans, 5% other)
Current leader: Queen Eyrian
Tech status: light industrialization
Magic status: very prevalent
The long-lived elves have always been patient, but when Emperor Basle began his invasion of Altza territory, the elves quickly proved to be a greater opponent than the humans expected.
The elves were slow to take up steam-tech, but after seeing the Empire's general success with it, they followed suit after a decade. They still don't use much steam-tech for war, as mages fill up the majority of their siege methods. Fire arms are quickly becoming very common amongst the half-elves and the occasional Steam Knight appears on the battlefield on the elven side.
Ascetics: Altza are heavily influenced by Ancient China. They like to use chinese long swords, bows, spears, etc. Guns are still at a flintlock rifle style at the moment.
Dwarven Merchant Guilds
Population: unsure (primarily Dwarven, but other races have joined)
Leader: varies from guild to guild
Tech: Heavily industralized
Magic: very little (dwarves make for terrible spellcasters, but they have mages in their employ)
The Merchant Guilds have done a great job of staying out of the war between the elves and the Empire. They've done such a great job that they're supplying both sides with weapons and equipment and profiting heavily. Thankfully, they have done nothing the egg on the conflict, but only stand to profit from it.
The Dwarves invented most of steam-tech. While the humans have improved upon the designed greatly, the Dwarves have learned to reverse engineer this improvements and further enhance their tech. As it stands, they possess the most advanced Steam Knights and have even created giant Steam Titans.
Population: varies from tribe to tribe (primarily beastmen, orcs, and humans)
The barbarian tribes are dispersed throughout the world. While they've stayed out of the war for the most part, a few tribes have hired themselves out as mercenaries. Some raid towns and villages for resources, while some are nomadic and avoid society at large.
Bandits, Raiders, and other Outlaws
Population: mostly human or half human
tech: low-mid (varies from one gang to the next)
magic: very low
Bandit gangs exist everywhere throughout the Empire and the world. Usually it's just rebelous folk who are fed up with the Empire, or those who can't make a living otherwise. What little Steam-Tech they use has been pilfered from their victims.
Council of the Undying
Population: unknown (99% immortal)
Leader: Four Lords who rule the Court
A tiny faction formed to watch over the world with undying eyes. Despite their name, most of their members are not undead, but rather immortal. Four Lords rule the Council at any one time, although no one knows their identities. Or their goals. Or even how they affect the world. But people suspect they do so from the shadows...
Population: less than a thousad
Leader: various druids and dryads
magic: very high
If anyone will be backing up the elves (and they have in small ways already), it would be the druids. However, they have been staying out of the fray for the most part. They've defended their own territories from the Empire, but never gone on the offensive.
Population: barely over a hundred
Leader: Supreme Paladin Shunaka
There are few organizations that are more powerful than the Dragon Knights. Their skills are second to none. They don't need tech or magic to do what they do - it's all spirital powers. They exist to deal with the world greatest threats, such as the Revenants and rogue Dragons. Because of this purpose, they have stayed completely out of the war. However, a select few have left the Knights to join their homeland in this war.
Asetics: Samurai style bad-ass-ness.
Population: a few hundrew
Leader: the Gatekeeper
The secretive Cataclysm Society exists for one purpose - to discover what caused the end of the Ancients. To this end, they have infiltrated the various other factions, as well as explored the Ruins as best as they can. While they have no interest in the outcome of the current war, individual members have their own plots and schemes...
The leader of this group, known only as the Gatekeeper, has appeared from time to time throughout history. It is unknown if it is the same person every time, or if the title is passed down. Either way, his influence and power is extraordinary.