So, I was sort of at a loss as to what kinds of societies to populate this world with! Then my roommate started talking excitedly about Aztecs, because that's just kind of a thing he does sometimes. Apparently the Aztec creation myth is that the evil gods murdered the sun's mother while she was pregnant, and he burst forth from the womb fully formed, fought all of them, and forced them to retreat into the sky. The Aztecs perform blood sacrifices to keep the sun strong because otherwise the Stars Will Return.
That seems like a fun foundation for a kingdom! Plus I think it's pretty rare for Aztecs to get to be the good guys, but in a world where evil is real and active, they're a lot more justifiable. Just have the sacrifices be voluntary and nonfatal- community blood drives to generate extra Divine Power.
Now, how much divine power should a nonfatal blood sacrifice be worth? Let's make two numbers real quick, a low one and a high one.
Lowball Calculations: When a human is killed, 10% of their divine power remains in the body. This means that 90% of their divine power exists tethered to the body, but not in it. Furthermore, since blood is only one part of the body, a lot of that divine power is in bones and organs. And, since we're not using ALL the blood, it's further subdivided. Our formula looks something like XP value times 10% times 30% times 10% (Portion that is in the body at all, portion that is in the blood, portion of the blood we're extracting.) a commoner is worth 5 XP, so a pint of blood is worth .015 points. Every 66 humans that do this generate one extra point. That's pretty underwhelming.
High Calculation: Just because 10% remains in the body after death doesn't mean that 90% of the soul's energy is free-floating. After all, if 90% of the energy is obtained in sacrifice, then THAT's the number we're looking at! Furthermore, if it's a willing sacrifice, then there's minimal reason to assume that there's a 1:1 ratio of mass to energy, as if divine power were butter spread exactly evenly over the body. If we really wanted, there's nothing to contradict the idea that people could bleed a very small amount and choose to trade away 50 or 80 or even 90% of their divine power by cramming all their energy into those few drops. That's kind of silly though.
I think a fair compromise is that the rituals of our Aztec kingdom produce, overall, 50% more Divine Power than a comparably-sized kingdom, and as such, they can support dramatically more divine classes. This is represented by having abour 30% more clerics, priestesses, and bladedancers, and dramatically more Paladins.
However, this is not without cost. In order to rapidly replenish the spiritual energy of the people, the Aztecs throw three festivals per season instead of one, and invest heavily into agriculture. This reliance on infrastructure limits their ability to expand, and their cultural dedication to eradicating evil wherever it may rise takes a heavy toll on their military. In short, they've got a really high income in basically every game resource, but they constantly spend all of it.
This is reflected culturally. They love bright colors, loud noises, strong drink, and give truth to the term "war party." They're also generally selfless, brave, and brash.
Finally, I want obsidian to do something cool, but I haven't decided what kinds of magical properties to give it.
Put all of this together, and you get a faction the players will almost exclusively hear about because obviously there's no reason to visit a small kingdom that's doing fine. Aztecs will show up other places, and generally make good allies, and obviously when we get to the Domains at War phase, they can be the cavalry that show up at the last minute to make a losing fight winnable. Because ever since I realized it was an option, my life goal has been to do this scene https://www.youtube.com/watch?v=kl5tG3fRZhk but with these guys https://www.youtube.com/watch?v=XUhVCoTsBaM
Also I should really think of a name that isn't Aztecs for these guys because it's important to at least rename the cultures you're stealing from for your RPG setting. I'm terrible with names, so suggestions are welcome!