The expansion focuses on adding content to the in-game time periods following the invention of gunpowder, and includes more general content such as 11 new scenarios, 10 new civilizations, and 16 new leaders.
Corporations become available with discovery of the Corporation technology.
The more instances of resources they consume, the more food, production, commerce, or resources they supply.
Corporations can be spread like religions (using the Executive unit as a missionary) to other cities, including foreign cities; any city hosting a Corporation branch must pay a maintenance fee for its services, while the owner of the Corporate Headquarters receives bonus gold for each branch.
Players can block foreign corporations from operating in their cities by adopting the Mercantilism civic, and they can block all corporations, even their own, by adopting the State Property civic.
Espionage's importance in Civilization IV has been raised to compare with that of scientific research, culture, income from taxes etc.
The new espionage slider allows the player to divert part of their income towards espionage activities against other civilizations.
Once the player has reached certain thresholds of espionage investment, the player starts gaining some automatic intelligence benefits over rival civilizations.
The player can also send Spy units into foreign territory to gather further intelligence and to perform various missions of destruction and propaganda.
Their role is a bit different, because spies are now invisible to all units, save for other spies.
Great Spies are born in cities, like other Great Persons, and can perform typical functions like serving as a Specialist, starting a Golden Age, or building a unique building.
Their special function allows them to infiltrate enemy cities, giving the player significant advantage in espionage against that civilization.
Just like other Great Persons, they have unique names, and their appearance changes accordingly to the time period, e.g., a Great Spy in the ancient era shows up as a ninja, just as the Industrial-Age Great Spy appears as a tuxedo-sporting James Bond-style unit, complete with similar thematic music once a mission is performed.