Quote Originally Posted by gardibolt
Even if they're excommunicated? Or don't they count as Catholic any more?

What about a crusade called against a Catholic faction?
1. (assuming city in question is not a Crusade target) if they are excommunicated it only means that the nobility has been a bunch of scalewags and scoundrels, but because the cities population is still of the same flock as you are you may not conquer the city. You may however assist an allied faction in taking the city, which maybe helpful to you and makes diplomacy mean something.

2. No good Catholic knows better then the pope, if he calls a Crusade on a Catholic City then Deus Vult (just remember that you are only allowed the city he calls the Crusade against).

Good luck