[2023] Best way to spread reformed Asatru into mainland europe?

Originally posted by AC Denton: Form Scandinavia or the North Sea Empire first. Though any Empire title will do. Crusades can only be declared against Kingdoms. If you're an Empire, they won't crusade you. Don't bother trying to invade mainland Europe until you have an Empire let you be constantly attacked.

Then to convert, just do it as you would anywhere. Do Duchy & Kingdom CB wars and grant those titles to dynasty members of your faith. They'll convert counties on their own. if you have any vassals that will be handed over to your newly-appointed ruler then take the opportunity to force convert them first, even if they get hooks.

1. Conquer the title
   
2. Demand conversion of your new direct vassals (accept hooks, possibly payments). Not all will convert but better than none
   
3. Hand the title off to dynasty member of your faith
   
4. Hand their De Jure vassals over to them once prompted

You now have a faithful vassal with their own faithful vassals whom shall all convert counties to your glorious true faith.

It's really straightforward honestly. Remember you can sail and raid up rivers. Focus capturing their capitals and capturing war leaders, which will net you that 100% war score.

Correction: Crusades can only be declared for kingdoms. As in, only kingdom-tier titles can be the target. You can absolutely have a crusade called against you as an empire, it'll just be limited to claiming a specific kingdom within your empire.