Well, I think it should be a bit more complex that that. Give kingdoms areas they can "Conquer and Hold", rather than just straight up "attack the city". Each area they control might contribute "resources" to the kingdom that's in control of them to put toward maintaining their army. On top of that, areas could also be "built up" with, well, buildings, that either alter the defensive capabilities of the army staying there, contribute more resources, etc etc etc. But then again, that could be getting into the realm of complex. There could also be different types of "units" that do different things better, but I think that was implied, with each Kingdom getting their own unique unit, or attribute, or bonus, or something.
Resources could include: Population (which can then be conscripted/recruited into the military), Food (for feeding your general population, and military), iron (for making hurty items), maybe some magic type runies (for spellcasters or, special bonuses, or something) and maybe even horses/animals/whatever that would be needed to "construct" mounted units, such as Cavalry or Gryphon Riders(in Calararian, though, cause they're the air power).
Say for instance, it costs, 1000 silver(cheap, I know, work with me), 7 iron, and 3 food (we're going subjective values, not kgs, or pounds, or ounces.... just, numbers....) to train a simple Soldier. Plus 1 "willing" population. The Chief Justice could then set how much silver the kingdom wants to put toward training Soldiers. When this amount runs out, the kingdom stops training them. The speed at which a soldier can be trained might depend on how many "Barracks" structures you have throughout the kingdom, or perhaps in a specific area. Say you have seven barracks, and that lets your kingdom train 50 units. Every hour (because, well, let's face it, immediatly is dull), your kingdom would then generate upto 50 new units, based on what's available for resources. This includes the iron, food, and silver.
As for what kind of troops you could have, well, I guess that's open for debate, but perhaps something like three variations of attack, three variations of defense, two all purpose troops, and a few cavalry (which might be used for attack, defense, or simply scouting). I'm throwing out random numbers, believe you me, I haven't thought any of this through at all.
As for what the other ranks would do... well... I'll let you guys bicker about that. Pfft. Building in areas would require silver, of course, available land (each area would have so much "improvement space" meaning, you'd have to pick and choose what you wanted there), some things might include a Fort, civilian housing, farms, barracks, mines, ranches(for mining horses), maybe lumber mills (to build, I dunno.. buildings?), quarries(building more buildings, maybe maintaining defensive walls?). A fort would plain and simple give the defenders a defensive bonus or whatever. ... I suppose that would mean we'd need siege weapons too... anyway, there you go. Blame me >P
Also, battles should be dealt out over a period of time, like, you set them in motion, they march X period of time depending on distance, then they battle and every so often the code checks down who dies, who lives, reinforcements can arrive so long as supply lines haven't been cut, etc etc etc.