Holy/Guild Wars

[PolarRaven]

The current system for war is "realm vs realm".  There is nothing in place that would allow for something like a religious/guild type war. 
I suspect that my idea would be a "coding nightmare" but I will bring it up anyway as it may lead to something that could be possible.

Under the current system, we have:
nobles join a realm
are placed in an army of that realm
are told that "*** (realm)" is their enemy
are sent to war to defend their realm or to defeat the other realms army(s).

The only real choice given to the player here is which realm they will join.

I will use Daishi/Mordok as an example.
What I see as being optimal here would be a choice of whether or not to join in a given war, regardless of realm. 
Daishi has many followers in many realms, but currently there is no way for these "religious nobles" to band together to pursue any given goal.
It would be great if a "Priest of Daishi" (or a guild leader/member) could gather followers from various realms to band together in a common cause. 
Not every noble of every realm that has Daishi followers, just the religious members that desire to see the "Priests" goals to fruition. 

Great leader's gathering like minded followers from around the continent for a specific purpose.
Find a suitable cause with a suitable goal/enemy, gather warriors that believe in your cause, and go to war for a "just cause" that you believe in. 
I think this could be much more satisfying than your ruler deciding what war(s) you will be involved in.

[Anaris]

I'm not going to say "never ever" to something like this, but it's definitely not something I'm going to be planning to include in the foreseeable future.

BattleMaster is designed around The Realm As Team. I don't see a compelling reason to change that, and I see various compelling reasons not to.

[pcw27]

If you've never gotten into a religious war you are missing out. I've had some good times with Turin and Sigurd. Auto De Fe's religious takeovers, persecuting heretics, regions going crazy when your religion is declared evil. I do however notice this kind of fun seems to be the exception rather than the rule for religions.

The problem is it's hard to get people to participate in religions. Church of Aaron took around a year to get up to speed. Now I hear it's basically dead. It has members but no one talks or anything.

I think the devs should consider increasing the paganism penalty. Officially paganism is a collection of peasant superstitions that are supposed to be shameful for nobles to believe in. Unofficially however it's really no big deal. I've never once seen a noble mocked or called out for being a pagan. The fact is it's hard to get people to check their modern sensibilities at the door and act like medieval nobles. That's why we need game mechanics that incentivize it.

Right now being pagan is a very minor drawback for a region lord. In fact they'll suffer worse penalties if they choose the wrong religion. A pagan region lord should get a message along the lines of "The region's lower gentry are horrified that their new lord believes in peasant superstitions rather than following a proper noble faith" and the penalty should be a severe. It could be a penalty to realm stats, or perhaps gold production with further flavor text explaining that many nobles are refusing to pay taxes to a pagan lord. Mere knights can be pagans if it pleases them, but once you're a lord it's time to get serious.

The other thing preventing the sort of scenario PolarRaven wants is that religions are usually highly regional, sometimes even directly tied to a realm. When they're more spread out the religion is probably so tolerant that no one feels threatened by it. The reason a lot of religious strife has happened in the past is that tolerance and persecution varied over time. In the Roman empire for example the Christians were relatively unmolested under the Antonine and Severan dynasties, and throughout the crisis of the Third Century. They were even able to openly build temples. Then the persecutions of Diocletian came around and that really got the Christians riled up. As another example in the middle ages Christian regions might have varying levels of toleration for Muslims and Jews. These groups might build communities for a time only to be driven out soon after. The same is true for Christians and Jews in Muslim lands.

[Medron Pryde]

I would love to see something like this.

The religious wars ideas.

I understand why it is low/no on the list though.  It would be hard to do.

That said, I would love to see more boosts/negatives for people who are part of religions.

Something as "simple" as combat bonuses if you are in a region where your religion is the majority religion.
Economic boosts if your lord, and knights, are part of the majority religion.

There are numerous small things that could bring the religion game a bit more into the life and breadth of the full game.