As it is implemented now, Broken Loyalties invites the following exploit. Cast the spell and take the best city of an opponent on the other side of the map. You won't be able to keep the city because you have no armies near it. However, what you can do is raze it or destroy every single improvement in it. Rinse and repeat. Perhaps it would be best to make the probability of success of the spell contingent upon the unrest and development in the city.
