Here's more detail for those who want it:
IMC I have a right proper religious war brewing in a post-Chaoswar DL-variant (My game predates all the 3.x DL materials by several years so think back to 2e supplements). The normal Gods have agreed to stop meddling in the affairs of Man on pain of death, resulting in the loss of all magic higher than 2nd level for all casters. Dragons took advantage of the power vacuum and took over about 80% of Ansalon. (Taladas is a factor in the game but is currently stable and looks much like the Taladas Box set)
Many years later, my players find and release a prior pantheon of divinities (referred to as "Spirits") that Paladine, Takhisis et. al. had locked away. These Spirits are able to grant all spells and reveal the secrets of higher level arcane magics.
Typically it is the poor and disenfranchised who follow the Spirits. And druids. Lots of druids. (There are many spirits that are the embodiment of primal concepts) Wealthy individuals have less need for external salvation and are closely bound to the Gods both by tradition and as the source for authority (e.g. the Knights of Solamnia). The existence of the Gods is not up for debate; the masses know they exist and the priests of the Gods have been healing people, creating water/wine, and performing (minor) divinations this whole time (0-2nd level spells).
Some authority figures are threatened by the perception that they may no longer have the right to rule (for instance a mayor who is appointed by the priest of Paladine) while others are threatened by the power the Spiritualists wield (primarily the dragons). So you have the classic trope for upheaval: a small group of individuals with far more raw, destructive power than their numbers would suggest opposing the entrenched society that completely outnumbers them.
The party cleric is referred to as "The First" and is held as something of a saint by Spiritualists but he has spent more time on teaching potential priests how to bond with the Spirits than on building any kind of church. The character will shortly be retired from PC to NPC to focus on organizing the Spiritualists and hopefully integrating them into society; or changing society, whichever works. Currently there is a loose "Council of Voices" that speak for the Spiritualists in one region but as yet there's no particular authority or compulsion for anyone to follow their edicts and some Spirits' followers do not have a recognized Voice.
(FYI: Traditionalist and Spiritualist gets shortened to the derogatory Trad and Sprite)
I've already got the standards of chaos and mayhem:
*lynchings of "heretic" Sprites by Trad mob
*vigilante Sprites appointing themselves judge, jury & executioner of criminals without regard for the law
*Trad merchants refusing to work with Sprite farmers or giving them poorer rates
*Trad nobles giving sweet-heart deals to other Trads or revoking the charters of Sprite businesses/organizations
*Various priests on both sides advocating both violent and non-violent opposition as well as those saying to "love thy neighbor"
*Some individuals think this is some sneaky conspiracy by the Gods to get past their oath not to meddle. This is not true but muddies the waters.
And a few not so standard happenings:
*The extermination of one entire Traditionalist hamlet through a slow-acting poison added to the well by someone under the effects of mystical compulsion. The puppet never saw his controller's face but believes them to be a Sprite, which means he refuses to be raised by them.
*The Towers of High Sorcery are deadlocked; recently the PCs allies staged something of a coup and simultaneously challenged for Mastery of several towers, following the traditional rules of ascension. This has somewhat paralyzed the mages as the Sprite Masters swore their oath of office "by magic itself" but not to the specific gods of magic.
*Raistlin is the spirit of magic. Long story short, the person who 'groks' a concept completely becomes the spirit of the concept, assuming there isn't one at the time. The three Gods of magic killed the spirit of magic long, long ago. Raistlin was the spirit of magic in the "Twins" saga, which is why he kicked the Gods' collective butts.
*Raistlin reassembled the 3 moons into one and engraved it with arcane knowledge. (He has his reasons.)
Right now I expect everything to blow up and possibly result in decades-long civil wars. I could forestall it with some divine intervention but the Spirits are recovering from their imprisonment and really aren't too well disposed towards the Races of Man yet. It's more likely the Dragons will begin a pogrom of their own and depending on the way that unfolds it could become Man vs. Dragon or Sprite vs. Trad+Dragons.
The King of Solamnia is generally open-minded about the Sprites, seeing it as a way to defeat the Dragons, but he will not tolerate anything that threatens his realm. He is a proper King who feels responsible to his people. The power of the Sprites could save them. The power of the Sprites could destroy them. He is currently walking careful road of diplomacy, trying to put focus on what it is to be a good Solamnic Citizen so that he can treat Sprites and Trads equally. (e.g. bad people get punished, good people are protected)
The highest level Knights of Solamnia find the existence of the Spirits intriguing but they are confident in their faith. They fear the chaos that may come but generally do not feel the Spirits as a whole oppose their faith. The lower ranked Knights are much less confident in their faith and are clinging much more tightly to the letter of the law than its (ahem) spirit. Some are enforcing the laws against worshiping "pagan" gods with a zeal, even though the King has rescinded those laws in favor of outlawing worship of particular deities.
