The Empire of the Northern Plains: Vilectine. Having a vast and powerful fleet of airships, the Vilectine Empire is easily the foremost of the three, and their emperor, backed by the Vilectine Senate, was the first one to float the idea of unifying the three empires in the recent aftermath of a disastrous war between Rabacci and Vilectine, during which the previous Vilectine emperor had succumbed to old age. Although he is in his early twenties and there are thus those who see his plan as rash, the emperor has significant support from older and wiser heads in the Senate as well, under the belief that war against an evenly-matched opponent is a folly of the past and that the advanced economy made possible by the airship renders such large-scale wars obsolete.
Vilectine’s heartlands are mostly flat plains, and they are famous for their powerful cavalry of all types, including heavily armored knights and their dreaded horse archers. Their powerful air navy is a heavy advantage, particularly with regards to giving casters exceptional range and a place to keep a giant stack of wands that’s close to the battlefield but basically guaranteed not to be compromised by enemy forces (so long as escort ships do their job, at least).
The Empire of the Eastern Seas: Chundao. The Chundao Empire primarily relies on its vast numbers to fight its battles. Although they are capable of some of the greatest feats of engineering and smithcraft in the world, the raw number of peasants available to be drafted and the efficiency of their supply lines (thanks to their famously effective bureaucracy) means that it’s typically wiser to equip their soldiers with cheap weapons and armor and then use superior numbers to outmaneuver the enemy. Reinforcing this is their regimented culture, which allows a fairly easy transition into military life when the time for a draft comes.
Chundao’s heartlands are on the coast of the ocean, and while their westernmost extremes include deserts and mountains, the bulk of their territory is out in the ocean to the east and south. A number of indigenous cultures there have been long since taken over by Chundao, and to them, the islands in the sky are different only in the kind of boat you ride to get there. Chundao has been hesitant to join the unified empire proposed by Vilectine. On the one hand, the benefits are obvious, but the Chundao are a people of tradition, and to merge their bureaucracy, administered by their emperor who is said to be of divine descent, with that of foreigners would be a heavy blow to their tradition.
The Empire of the Western Mountains: Rabacci. This desert empire is run by a collection of merchant princes, whose vast wealth is built atop their gold and mithral mines. Although their armies are not particularly exceptional offensively speaking, the extensive fortifications in their homelands make them nearly immune to retaliation even from other empires. Nonetheless, war is costly and often not good for the ones fighting it, but very profitable for those on the sidelines, and thus Rabacci prefers to see Chundao and Vilectine go to war rather than get involved themselves.
Rabacci is mildly theocratic, in that they require all of their subjects to at least give a token show of worship towards Thanatos, but this is mostly just a relic of ages past when the various lands now ruled by the Rabacci guild lords were theocratic or feudal states. Nonetheless, the entrenched religious mindset of the peoples of the heartland of Rabacci makes the guild lords hesitant to merge with the other two empires as per Vilectine’s request. Despite the obvious advantages of being members of a superstate (particularly since there is no chief executive of Rabacci and thus individual guild lords have little to lose), the unrest of handing over 2/3s of the nation’s sovereignty over to heathens could destabilize the Rabacci.