From a great big interview about Civilisation IV:

IGNPC: How do governments work this time around?

Barry Caudill: There are no set governments anymore. In Civilization 4, you can choose from various civics and combine them to make the type of government you want…In addition, AI leaders will have certain favorite Civics and they may ask you to either switch to theirs or stop using the one that offends them.

So you too can export freedom, democracy and market economics! This system will also work in terms of simulating religious tension and conflict, a long-overdue addition to the Civ game.

But what about other means of ahem ‘influencing’ your fellow powers? The world, it seems, has changed since earlier Civ games…

We will not be including any espionage options that are terrorism related.