The good news is...I found the game!
The bad news is...I found the game, installed it, and it works!
At least I can't be addicted forever. While I looked it up and apparently there are cheat codes, at least during scenarios, the cheat codes don't work. Meaning that the only way to beat the RIDICULOUSLY-hard campaign is to...fair and square, as intended, beat the ridiculously hard campaign which I was never able to do! So my addiction to it is gonna be short-lived.
Anyway! The name of the game is Nemesis of the Roman Empire. It has four civilizations you can play as. Romans are one, haven't replayed them but by memory they've got the toughest, most expensive units in the game, taking time to build up a force but dominating once they do. Carthage is a second one. Not sure which they are, if they're the civilization using the desert-theme or if that's the Iberians, but whichever uses the desert theme, they rely a lot on gold, except for Elephants. Their units are expensive gold-wise, but cost very little relative to the Romans if memory serves, especially with strategic usage of the blacksmith.
The third civilization I believe is the Gauls. They were the tutorial civilization...I think. Two civilizations are vaguely similar from memory, I just don't know which two they were.
Anyway, the civilization of the tutorial, whatever it was (stone-structure-based), is food-centric in contrast to the desert-themed's gold-centric. Most of their units are cheap, costing very little gold, but use quite a bit of food.
The game allows units to level up; units that level up gain health primarily. The game also allows units to have items, with items often granting some sort of bonus, with some items able to be used, like healing water. A major mechanic of the game is that units can be assigned to a hero, becoming a higher level and getting an experience bonus when attached to one. Heroes also serve as major unit hubs as a result, efficiently transporting them together, and serving as great ways to keep track of several things at once.
There's no building buildings in the game. Instead, a major component of the game is capturing buildings, that start with a loyalty. When loyalty reaches zero, the building converts to be on the side lowering its loyalty. Loyalty doesn't lower if units loyal to the building are nearby.
Another major aspect of the game is that food, in addition to recruiting units and being used for various upgrades, must be fed to units. All units have a food rating. When they get to 0 food, they slowly begin to starve, losing HP. (I believe the minimum is 10% of their full health. They cannot die from starvation.) Units do tend to heal when well-fed though, at least most seem to. There are, of course, healing units to speed this up.
All in all, I have very fond memories of the game, but while playing single matches is all nice and fun and all, the campaigns each feature at least one level that, where if you make so much as a single mistake, you get overrun and annihilated in short order. Seriously, at one point, I remember even looking up a walkthrough for one of the levels, and the strategy the official walkthrough gave was basically, "Do what you were doing, just...do it better, and faster, with greater accuracy."
No, seriously. Keep in mind that by the time I was even trying the campaigns, I had played many matches on single-player with tweaked difficulties here and there. Still didn't make much of a difference; I got massacred. If memory serves me, not on the first level of the campaign. Oh no. The campaign lures you into a false sense of security by giving you some easy missions any ol' player can complete just fine...and then...BAM! MOTHER OF GOD, WHY ARE THERE SO MANY UNITS COMING AT ME OH GOD I'M GOING TO DIE WHERE DID THESE GUYS ALL COME FROM?!?!?
Granted, this was years ago, so I don't know how I'll fare with more experience.
...However traumatic my memories were, I vastly underestimated how bad it was.