I'm A Banana
Potassium-Rich
It's never seemed to me like a good hook for a D&D adventure. What motivates a rational PC to get in the middle of a cosmic war between the primal forces of ultimate evil?
The people who get in it's way.
A common trope in my 2e PS days was "The Blood War is spilling out onto this land, which is caught in the middle. Go there and help the people survive!"
There's also the war machinery that it requires. Devils seeking long-lost artefacts, demons releasing gods of pure destruction, all sorts of great "Stop them from getting the McGuffin!" missions.
There's recruitment. Devils corrupt powerful mortals to serve in their armies, demons tempt them to do likewise.
Any plot that puts the PC's in between two nations at war can work with the Blood War, with the caveat that peace is almost worse than conflict in this scenario.
The Blood War makes Demons too lawful. I sometimes see references to Demonic "generals" and "enforcers" in various splatbooks. Or I read that such and such a demon is tasked with "rounding up stragglers trying to avoid duty in the Blood War." I read about Abyssal layers that serve as foundries, shipyards or mustering grounds. It just seems to organized and methodical to me.
I will tentatively agree with this, but it's easy to make them more 'organic,' more like a gibbering hoarde of destruction and less like an organized force. Still, the more intelligent demons know how to best use the tools at their disposal -- chaotic demon doesn't always have to mean 'mindless killing machine.'
Mourn said:(alignment) makes assumptions that don't hold up if you intend to have any sort of realistic moral complexity in your games.
Wrong. Totally, 100%, dipped in wrong. Full of wrong like a pinata filled with razor blades. Wrong. Wrong. Wrong.
Well, okay, maybe it was true in your experience, but I submit that your experience was unfortunate.
(law vs. chaos is) important enough for evil to be fighting the longest running war ever? See, that strikes me as... well... unbelievable, because it depicts good as incredibly wise and evil as incredibly oblivious (thus, contributing to evil losing because it's dumb).
Law vs. Chaos is just an excuse. Evil fights evil. Evil fights EVERYTHING. Evil is its own greatest enemy. Good is its own greatest ally, but even Good creatures have deep disagreements about what it means to be truly good. These disagreements don't usually dissolve into war, because as much as they think the other team is wrong, they show compassion, respect, temperence, and other virtues.
Evil has no virtue. It has cruelty, dominance, rage, and other vices. It has no reason, motive, or desire to ally with anyone or any thing. This is why it is self-destructive. Some of the more brilliant demons and devils probably know this, and that's why Asmodeus, for instance, was never really deeply invovled in the thing. Some of the more brilliant celestials know this, too, but Good people tend to believe other Good people when they tell them things; Evil people tend to mistrust everything.
Evil isn't dumb, but it is evil, and HATE is a defining characteristic of it. That hate is universal and absolute. It takes consumate skill at evil (e.g.: the status of some of the Demon Princes and Lords of the Nine) to control it and direct it constructively.
And, heck, I never thought of the Blood War as a war of extermination for either side except on the level of 'common field grunt.' I thought of it more as a proving ground and training ground, a place where violence could determine the worthy and the powerful, so that greater evil can be distilled from the crucible of conflict. It was in the interests of the orchestraters of the Blood War to continue it, to make evil as a whole stronger. And when Good had no one to fight, Good would become weak and complacent, setting up a greater overthrow (eventually) than either would achieve on their own.
In almost every single example I can think of where evil turns on itself, it's after it has become monolithic and victorious, not in the middle of the epic struggle of good and evil.
You're thinking in pretty narrow terms. For one, most of the D&D planar fluff didn't imply much of a current struggle between Good and Evil. Largely, Adventurers did that, and they did it on the level of heroes and villains, not on a cosmic scale.
For two, it is possible that the Blood War occurs either (a) before Evil has had a chance to grow monolithic, or (b) after it had already become monolithic, and it just hasn't stopped yet.
In a lot of fluff, Asmodeus is almost the *progenitor* of the very *concept* of evil. Perhaps in ages long bygone, it ws good vs. evil, but then evil turned on itself...and it's still turning on itself...
And maybe that's intentional. Maybe they realized they couldn't take Good unless they were strong and Good was soft.
So, instead of being determined by your actions, it was primarily determined by your parent's address. It's dull.
A lot of Real World sociological theory goes into figuring out exactly how determined your actions are by your parent's address.
Let's just say my life would have been different had I been the only child of a rich banking couple in Beverly Hills.
So I disagree, the tension between alignment being a choice or being culturally determined (or being part of the very fabric that makes you up) is a delicious tension with many deep psychological roots.