In my opinion the option of vassal states comes to late in the game. Usually they come between 700 and 1100 AD which is understandable as in reality thats when feudalism evolved and the whole lordship thing began. But look at for example at the Persian Empire in 500 BC. How would the way they ruled their empire be called than? They conquered their neighbors and installed a local king of themselves who was to be the puppet of the King of Kings himself. Almost all local cultural habits and religion was left in place they were just to supply tribute and military when required. Some kingdoms were just requested to give the King of Kings water and land as a token of their obedience only by threatening them with military might. And many did so. All this seems to me like a similar system as how vassal states work in Civ4. Although it is not so clear at all how these two relate exactly, to me the Persian system of satraps and vassal states in Civ4 show many resemblances. Thats why I plead for a similar system in Civ4 or for an earlier option of vassal states. As I like to build huge empires right from the ancient ages on, I really miss a feature like this. So many times I've wanted an AI to capitulate to me but instead I could only make peace with them couldn't even demand a thing because all these features aren't enabled yet. In civ4 I want to be able to be the King of Kings right from the 2000 BC's and on!