Hmmm...
Well, I think that it is a valid thing to superimpose common culture onto that of Zeal. After all, the situations may change, but human nature does not. The way Zeal begins to worship the Mammon Machine, for example, strikes me as similar to the way in which the Israelites forge the golden calf, and thus begin to worship a god of their own making, and the Devil through it. Though they lived in a grand kingdom, the people of Zeal would have behaved no differently than any of us in the same situation. As they say about power, it corrupts. Now, I pray your patience, but I have always seen Zeal as similar to Tolkien's Numenor, not least because they are both a version of the Atlantis legend. Moreover, both are destroyed in the quest for immortality. I've mentioned that time and again, so I won't repeat myself more. But the point is, I see the military of Zeal in something of the same manner. After all, who could oppose Numenor? What enemy did they have in all the world? Sauron lived, yes, but not until the very end did he show his hand. Why then the great arming of Numenor? Because they turned on the West: they, by the guile of Sauron, began to see their allies and friends as foes. As Elendil says, 'we who have no enemies are embattled with impegnable fortresses, and mostly on the west...'. Those with no foes begin looking for them. And as for the earthbound who are opressed... it's yet another similarity. Those of Numenor began to opress the lesser people of Middle-Earth, demanding tribute and finally enslaving them. It coloured my perception of Zeal, actually, and I see Zeal as having a similar history. I think that, at first, they were good and gracious (as most things begin, with good will), but as time went by they became corrupt and opressive. Thus we have the hosts of Zeal. Schala in my fanfic speaks of it at length, and pretty much sums up what I thought of the Zeal military. Here:
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"Ah, Zeal! How clearly I yet remember your splendour and magnificence! Ai, es meredet malecho! Serge, nothing seems magnificent to one who has once seen those towers. And the armies of my land, one hundred thousand strong, against which no foe could stand. Not merely dauntless and valiant, but so wondrous and beautiful to look upon: our spears, whose heads were cut of flawless diamond, shimmering as fields of crystal in the midday light; our swords, woven with enchantment which no malice could undo, shining pale in the twilight as the sun crept below our horizons; and the golden helms and gilded coats of mail of even the lowliest soldier. When the war trumpets of Zeal sounded aloud it was a symbol of fear to all the earthbound kingdoms, and even the mightiest land trembled at the very rumour of our coming. For to them it seemed as if the very heavens broke open with thunder, and gleaming legions of angels descended; so magnificent were the hosts of old Zeal. And so by the time of my life there was no enemy to Zeal in all the western world. Beneath our heel we held subject all the lands of the west. Some might say with stern yet benevolent lordship, while others would name us tyrants, oppressing all beneath us. For what I knew, we were some of both. At times our great masters of lore would come among the people yet lacking any strength of sorcery, and teach them what they could of our knowledge. But as the years lengthened we became cold and stern, and tired of the life granted us. It was not our beauty that diminished; that grew till the very hour of our destruction. But on a time the forums of Zeal were thronged with multitudes, not only of Zeal but also of the earth. It was partly by their strength that the Arythfala, the Pillars of the Stars, the beautiful towers of the citadel, were raised. However in the last days to which I belonged no earthbound could so much as peer up at the Kingdom without fear of punishment. And this was at the command of my mother the Queen, and few dared oppose her in word or action. Her three counsellors, the great Masters, did so, and thus they were banished to far flung and woeful prisons. I also worked against her evil, though being but a child did so more in secret, and through an indirect hand. I alone of all the high Zeal court yet visited the lands beneath, to bring my learning to those unenlightened that lay under our rule. But I did far too little, and was blind to how far things had come, because for all our might, we crumbled at our own hands. Our grandest legions could not forestall the enemy that we became unto ourselves. And in my weakness I did not, I could not, oppose this nearing end."
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Remember as well that I think that what is shown is but a small portion of the world. There are lands far east and west which, for many hundreds of years, the hands of the Zeal Kingdom could not touch. They were a land that was upon the air, thus unassailable it is true (and thus having a great advantage in matters of war; they could fully empty their land without fear for retribution... mostly.) But how big is it? I don't think it's more than 100km across, which is quite small, really. In time it probably drew into alliance, and later absorbed, those lands about it (like Rome did with the Latin League), eventually gaining power over the whole of the West. Those who had skills in sorcery were likely welcomed into the high court, whilst those without were made to toil in the silver mines and what not (after all, Zeal is not that large, and only the mightiest would be allowed to dwell on it.) Finally, this bred arrogance, and absolute oppression. But I stray away from the topic of the military.
Zeal did not all at once have dominion over the world. It needed to conquer. And thus the army. Now, in history, the military is very powerful usually. Take Rome: often the generals had enough support from the legions to have themselves declared emperor (at least in later times.) Thus even after there is no foe left in any near land, and they control the greatest empire to ever be (not just the land of Zeal itself, but a vast area all about the world), the military would not disband. Firstly, they are not fully invincible. Secondly, as has been said, rebellion must be quelled. And thirdly, you CANNOT simply tell a general and his legion of thousands of soldiers to disband. What would happen? Civil war. They would march up your forum and take your capital by force. Therefore the military remains, if for nothing else than for itself, and by the time of the Ruin is quite impressive, though mostly for show.
Well, that's how I see it. As you probably know by now, my imagination is a rampant thing, and I take much artistic license.