I don't like that idea, sorry.
A "monopoly" is not something someone accepts (voluntarely).
It is something that is forced upon someone.
However, this could be implemented:
1. The only way to "break" that monopoly would be to conquer the city that has built it.
Variant A:
Main seat of that organization is taken and now the monopoly has a new owner.
Variant B:
The organisation is destroyed and any civilization may try to build it again.
2. Every monopoly you have (Fur, Cotton, Gems, Walruss-Ebony, ...) will make the other players (European AI) a little more angry.
-> If you have assembled a lot of them, the AI-Players (Europeans) will very likely declare war.
This would become an extra aspect in Attitude (Diplomacy):
"Your monopolies threaten our economy."
The more power -> the more enemies.
