I don't remember a difference in loyalty from destoying foreign buildings, there may be one, but it is not shown as it is in RTW. If you want to make a difference in how well the other factions recover from your raids you could build watchtowers or borderforts in the provinces you take over. Leave the next turn and the loyalist rebellion will have a higher loyalty base. If you want to make it even harder you could build two turn buildings to help the enemy build better troops. Remember the more money they put into building churches the more money you get from viking raiding.

mfberg