When a CS is near and other civs place their Amanis there, the -2 effect of Amani can sum up to -4, -6, -8, ... depending on number of Amanis with promotion. This can destabilize a small nation near the CS very quickly. I just see small Poland (world map) loosing its cities to Russia one by one due to this effect. (In a game with 30 civs it is more likely than in a small game.)