To make it simple, the
Monopolies and Corporations mode allows to establish national
Industries over a Luxury resources to enjoy additional yields and modifiers, founding international
Corporations for better yields and modifiers, create
Products for even more yields and modifiers (and some Tourism), and securing
Monopolies to generate Gold and Tourism.
There are some key points:
- The Currency technology: it allows to establish Industries. You need a Builder charge, and control at least 2 luxury ressources of the same kind. You can only have 1 Industry per city, but all civilizations can have an Industry of the same Luxury resources. It gives some yield (2 Food, 2 Production, 1 Gold, 1 Great Merchant point) and a modifier, which can be either +15% Science, +20% Culture, +20% Growth & +3 Housing, +25% Faith, +25% Gold, +30% Production (military) or +30% Production (building) depending on the Luxury resource.
- The Economics technology: it allows to found Corporations. You need a Great Merchant over an Industry, and control at least 3 luxury resources of the same kind. You don't need a Monopoly in order to create a Corporation, but there can be only 1 Corporation in the world. It is possible to remove an opponent Corporation if you happen to have a monopoly on that resource. Corporations give some better yields (4 Food, 10 Production, 3 Gold, 2 Great Merchant points) and a modifier which is the double of the Industry, so either +30% Science, +40% Culture, +40% Growth & +6 Housing, +50% Faith, +50% Gold, +60% Production (military) or +60% Production (building) depending on the Luxury resource.
- With a Corporation, you can now do Create a new Product projects. Once done, it will generate a Great Work "Products" that can be slotted in a Stock Exchange or a Seaport building. Those buildings have 3 slots each, and a Corporation can generate up to 5 different Products. They each generate 1 Tourism, 2~6 yield, and a modifier equal to an Industry. They stack: it is possible to achieve +120% Science or +200% Gold in a city with a Corporation and 6 Products.
- The Mercantilism civic: it allows to know how many Luxury ressources exist in the world, therefore know if you are close to a Monopoly or not. A Monopoly allows to gain Gold and Tourism modifier, and you do not need to wait to unlock the Mercantilism civic to enjoy from Monopoly's bonuses: the Civic just allows to know how many Luxury resources there are in the world.
- A Monopoly is reached when you own at least 60% of the Luxury resources, and will start to generate Gold or Tourism:
- Gold: you will gain 5, 10 or 25 Gold per turn and per Monopoly if it is a 60%, 75% or a 100% monopoly.
- Tourism modifier: It is applied to all players and depends on how many Luxury resources you own, and how many opponent doesn't own the luxury resources inside their territory. A monopoly of 5 Amber resources against 7 civilizations where 5 of them don't have it is a 5 × 5 = +25% Tourism modifier, applied to all 7 civilizations. That Tourism modifier is tripled (→ 75%) if you own an Industry or a Corporation.
Personal thought:
As you can see, the yield modifier from Products are quite borderline, but are at least limited at 1 per city and 5 Products per Corporations. Meanwhile, the Monopoly effects are completely broken.
Gold-wise, if you happen to start alone on your own small island/continent might give you a full Monopoly of 4 different kind of Luxury resources. It means you will enjoy +100 Gold per turn at the beginning of the game without much effort.
Tourism-wise, since it scales with the number of opponent, the bigger the map is, the bigger the Tourism modifier becomes. Owning a single monopoly of 6 resources on a Huge map against 11 opponent means you will enjoy +198% Tourism against every civilizations. Many people ends up winning a Cultural victory by accident.
The
Monopolies and Corporations is a great idea, but poorly executed
(as stated by @Zaarin). It is also a "rich gets richer" game mechanic. When the game generate a map, it puts 4 kind of Luxury resources per Continent. Taking over the continent, either because you started there alone or through war, means you will own 4 full monopolies, meaning you will enjoy 100 GPT and an absurd Tourism modifier until the end of the game.