The campaign game in M:TW is almost exactly like a game by Games Workshop (creators of Warhammer) called Blood Royal (or Blood Royale can never remember if it has the "e" on the end).

This game consisted of a map of Europe (well, Eng, Fra, Ger, Ita, Spa), each country divided into territories, some territories providing tradable goods, etc. There were shipping routes, taxes, troop raising, Kings, Princes, Princesses and the Pope! There were rebellions, plagues and crusades!

I'm almost positive that M:TW was based on Blood Royal.