As the industrial ages came upon Europe, all the nations of Europe became interested in preserving the status quo. that is, they would keep each other from getting too strong or too weak. this is what happened in the crimean war against russia, and most other wars that defined this age. after the discovery of nationalism, nations were no longer interested in completely taking over each other (other than a few exceptions) because they would not be able to handle the revolt, and they would usually grant them independence for a hefty price. this is what happened in 1871 after germany defeated and france, and also in both world wars. the losers were granted 'freedom' for a huge sum of money, all their colonies, and a passive govt that could be easily controlled. i want to see this in civ. after we get nationalism, the computer should not allow for an easy takeover as it does in civ 3. if we try to annex the land of an equal country and people (like the europeans considered each other more or less equal in status because they were all white, but discriminated against the others), then there should be a massive revolt and all the other countries (enemies and neutrals) should get pissed at you and they should actively try to persuade you to reconsider (through diplomacy or even war if its that important). note that this would not apply with the colonies (backward civs) unless ofcourse your enemies don't want you to get too powerful, in which case they should be able to choose whether they should help the weaker civs or not.
i know this is kinda far fetched even for civ 4, but it is very possible in one of its expansions, like we had new things in conquests. what do you guys think?