Aarn has always suffered from a massive poverty gap due to the low population density and high mortality rate. Arguably, this was at its worst at the height of the Jerol empire, when magical guilds kidnapped children who showed channeling potential, and where the science of wizardry was a closely guarded state secret. Most people did not have access to magic nor education, so while the aristocracy of the Jerol Empire flourished, the plebeians stayed trapped in the dark ages.
During this time it was fashionable for high-class adventurers and Jerol officers to use plate mail armor. It provided a decent protection against most threats the then-current environment presented, and also helped create an imposing psychological presence.
When the Empire collapsed, the channeling guilds collapsed with it, and the technology of magic began to spread throughout the realm. Five-and-a-half centuries later, plate mail has become obsolete. Monsters, magic and mayhem have made mobility in combat more important than an ability to absorb blows. While obsolete, plate mail as a technology is romanticized and it is still available. It is also a part of the military regalia of Cerenbaun, and worn by professional guards and mercenaries who do not have to do much traveling or who have little to no chance of combat. Plate mail armor is seen more as a romantic status symbol than as a genuine, practical method of protection in combat.
Most adventurers wear leather armor; anything heavier would hamper their mobility too much in dungeons, swamps and forests, where most of their violent encounters take place. There are also magical equivalents that help protect adventurers as much as plate mail would, but without hampering mobility. Common items are magically treated cloaks and amulets that provide a field of protection, absorbing blows.
The Cerenbaun army has come a long way since the knights and foot soldiers of Jerol. It's subdivided into smaller units that resemble adventuring parties, forces that are heavily enhanced by the ability to cast magic and the supply of magical items. A military unit usually has two wizards, two channelers and two healers, though these jobs often overlap allowing individuals who do or cannot use magic. Stealth and subterfuge are considered more important than direct combat, and the fighting unit is designed to hold their own or retreat in the face of overwhelming odds.
For battlefield combat, Cerenbaun foot soldiers are usually armed with medium armor, a shortsword, a wand of randomly selected ranged magic, and a short bow or crossbow with arrows. Standard equipment also includes an amulet of protection, a ring that cleans and provides hygiene, several healing potions and several grenade-like potions. Specialist units are armed with pole arms, longbows, tower shields and other similar items. Occasionally biomantic monsters are inserted into the ranks, but such units are usually used as expendable berserker units who are sent in to soften up and intimidate the enemy before the main force arrives.
Cerenbaun siege engines are animantic and usually their soul cores are attuned to the individual drivers and unit commanders who are well protected. Cerenbaun's tools of war resemble bipedal tanks, huge trebuchets, and mobile fortresses where the commanders of the battle can congregate and prepare their battle plans. Avian units are rare but not unheard of; they are usually relegated to scouting and fire support rolls.
Field battles usually take place with around one thousand soldiers on a side. During the age of the Jorel Empire, forces of 5,000 or more were common, but the low population density made recruiting that many soldiers difficult, even then. In contemporary times, Aarnian military has focussed more on the style and strength of the army's magical technology than the number of soldiers.
Flintlock and blunderbuss pistols are beginning to develop as a technology, but they've yet to fully catch on. People without magic usually do not have the education to create them or the gunpowder they require, and guns themselves are inferior to most magical items that do ranged damage. Hand cannons are usually used by ne'er-do-wells who typically use them as weapons of last resort that cannot be detected by magic.
Most of Zenninfall follows in Cerenbaun's footsteps when it comes to military technology, especially the areas that were a part of the now-fallen Jerol Empire. Other areas are not so similar. The environment of Western Habruk is harsh and unforgiving, making large-scale combat both impractical and costly, so Western Habrukkan wars are usually fought with war bands of 80 people or less. Igakari's military focuses more on police action than invasion, forgoing seige engines and foot soldiers for state-sponsored guards and constables who have a defensive role in mind militarily, keeping the outlaws from the Eastern Border region from invading Igakari. Igakari also has a powerful navy which they use to influence and keep in check the Kaipu peoples from the Eastern Islands.
The isolation of the Kaipu races that live in Eastern Habruk has allowed them to develop a somewhat unique military style. The mainland Kaipu forgo magic in combat as dishonorable and sacrilegious, preferring to use magic for household tasks and religious ceremonies. Their military instead focuses on foot soldiers armed with long pole arms, spears, and longbows. Despite living in the mainland, the snaking rivers of Eastern Habruk have made a navy quite important, and the Kaipu forces will often fight with one force on land and the other force in the river, the pole arms allowing the units to attack one another despite the short distance between the almost-beached river-boats and the units on foot on the shoreline.
The isolation of the Rensvaja have also allowed them to develop a military style that would be strikingly alien to Cerenbaun forces. When war breaks out between the various Rensvaja kingdoms, the kings themselves go to the battlefield and fight one another directly, using their channeling magic. Disputes are thus settled by these champion kings proving their might through magical combat, which is part of which what makes their massive soul-linked collectives so important to their culture. The fights may be superficially one-on-one, but the kings' families, retainers and spiritual advisers are all aiding the fight by lending their magic to the king through the soul-link.