Doesn't this necessitate that the priests were first imprisoned? and doesn't it follow that they must have been in a land where they were uninvited?
This precisely. And you can't ban priests unless they are caught in the act of doing something nasty. SA priests had nothing to do there, it was clear they were just setting up the grounds for an invasion, as all leaked messages from SA clearly paint.
Notably SA's will to have it illegal for any realm to banish SA priest preaching, lest all the SA realms invade. Obviously, non-SA realms don't like this.
