How to spread custom religion fast?

[Future Doctor]

I made a custom religion, how do I spread it to other realms? I've won many holy wars against me and gotten a lot of prisoners. I can demand conversion of some of them and release them but I can't demand conversion of mayors, dukes and kings (The ones with the titles). I pinned some of the prisoners I set free and noticed some of them reverted to their original religions and my custom religion still has not appear in other realm's counties.

Now my realm and my counties is basically fully my custom religion through my court chaplain but it doesn't get any bigger than that. How do I spread to the other realms fast?

[Kapika96]

What was your old religion?

Your new religion is technically a heresy of that. So if your old religion has low fervour then there's always a chance your new one will pop up in a heresy event and spread that way (worked for me when I switched from catholic).

But if your religion isn't an offshoot of the neighbouring religions then you'll probably need to conquer stuff to spread it.

[CrUsHeR]

It is not a custom religion, but a custom faith of your former religion, based on your former faith.

This also means that it might spread as a heresy outbreak for anyone in the same religion, potentially flipping entire realms. But otherwise you need to spread it through war.

[Future Doctor]

Ok my old religion is catholic. I am getting wars declared on me by both catholics and ash'ari rulers saying "My false religion has kept your subjects in the dark" and I have been getting a lot of prisoners from the wars.

I demand conversation and release them for the ones that I can, and behead and devour ones that I can't. (Because their demand conversion box is greyed out) My custom religion is not spreading outside my realm. There has to be another faster way to do this other than conquering.

[jessemode]

I am playing with a tweaked faith for the first time and have been wondering about this as well. Now that you cannot demand conversion for landed prisoners as a release from prison option, it has gotten a lot harder to convert other realms.

Then I started really exploring intrigue. Get the kidnapping skill. Shop around other realms looking for someone that has an unlanded heir. Kidnap the heir. Then you have some options. I do NOT recommend immediately demanding conversion and letting them go. I tried this for a while and they usually convert back to their old religion shortly after getting home. You can force convert them and recruit them to your court. Then they are nice and safe under your thumb until their original liege or daddy or whoever kicks the bucket. Then they go home to rule as a member of your own faith. Sometimes this works well, sometimes they get offed in internal wars.

Another option I love is: once they are a member of your court, if they are single you can have them matrilineal marry one of your daughters/female house member. If they are married, you can plot to kill their wife in order to free up their "hand in marriage". If you go this route, you can be allied to them when they go home and assume the throne. This will enable you to help them fight their internal wars and actually keep them on their throne so they can *hopefully* spread the religion. Another advantage of conversion + matrilineal marriage once they are your court member is that this also enables you to put your house members on foreign thrones.

Just a few things to remember: don't try this with landed heirs as you cannot recruit them to your court or force convert them. Also, don't try this with someone who has the zealous trait. You cannot force them to convert either.

[Kapika96]

Originally posted by Future Doctor:

There has to be another faster way to do this other than conquering.

Conquest is the main way that christianity and islam spread. They're also the 2 biggest religions in the world.
That's definitely the fastest way, as it should be. I mean, why would they listen to you and switch away from their current religion unless you have the power to force them to?