Here’s a flowchart I made for making the simmering religious conflict that Gary talks about in T1: The Village of Hommlet come alive. And, by “alive,” I mean “escalate until one side is dead.”
You can think of this like an encounter that happens every time the players return from adventure; or you can think of it like a Front from Apocalypse World.
The point of using this procedure is to make the game world more compelling. It is independent of the players. They can choose to ignore the conflict as they wish; you, as the DM, will ensure they witness what’s going on by having these events occur in their presence.
If the players intervene, you may have to modify the events. Many or most might not happen, or different NPCs may need to be involved (say, if the players kill Jaroo, Calmert, or Terjon).
Similarly, you could use this for any generic religious conflict, not just for the one Uncle Gary gave us. Something happens, and one side esca-retaliates, and then the otherside does the same until there’s nothing like to retaliate on. That is, unless the players intervene and change the course of fictional history-in-the-making.