Ok, to recap:
Fintilgin has made some very good points about city-flipping; I agree completely about how frustrating it would be to automatically lose cities simply to replay history. Rhye's mods (at least my old favorites, RoC and RoCX) nor the Civilization game as a series have never been about simply re-creating history. The most important things are fun and feasibilty. It's also good that the mechanics of the game are easily explained; Blasphemous' first suggestion seems near-impossible to decipher in-game, compared to culture. On the other hand, I agree completely that it was not always attacking barbarian hordes that formed a new civilization; RATHER...
*dramatic pause*
It was a NUMBER of DISTRACTIONS that kept the original empire busy when a new civilization was forming!!! Think about it; Rome was founded when Greece was over-extending itself in trade and colonization of the Mediterranean. America was formed in revolt, but because it was far away from Britain, under its cultural influence less, and there was a lot of unhappiness due to taxes. Spain and France have direct roots in Roman conquests, and started becoming a civilization after Rome was trying desperately to fend off the Huns, Visigoths, etc. So what does all this mean in Civ terms?
Rome: Greece had too many cities, too high maintenance, so even a close colony split off.
America: Far-flung colony, little English culture built up, too much dedicated to taxe slider rather than culture.
Spain, France: Barbarian horse archers pummeling Roman cities (several were taken and razed, IRL), people of even nearby European colonies on the frontier became fearful, demanded greater military presence; none came, cause of unhappiness maybe? Eventually cities fell to barbarians, taken (if in capital location) or razed, then new civ springs up in their wake. Thus the decline of Rome!
And our classic example, Arabia:
Arabia: Jerusalem was fighting ground against barbarians for many turns, continuous un-repelled attacks (from barbs ONLY) means discontent. Arabia springs up with new religion, but LITTLE STARTING CULTURE, to match history. Instead, they get one city, MANY starting attacking units, and missionaries. The way is open for them to make peace with their neighbors and try to spread their religion, or use force and attack neighboring civs with their starting Camel Archers as happened IRL. They can even, say, make peace with Egypt and attack India, or vice versa. They don't need to start with many cities; historically they didn't, anyway.
SO! What's this mean for actually making it happen in game? What are the variables?
Chances of a city flipping go UP with:
Total discontent
Distance from city
Total maintence costs of ALL cities (and/or total number of cities)
Barbarian attacks that make it to a city (so it's beneficial to attack barbs in the field rather than have them suicide on your defenses)
Ongoing foreign wars (more troops in enemy territory than in own territory; neutral lands count for neither)
Chances go DOWN with:
Military presence
Culture in city
Higher culture rate
Good foreign relations
Tech superiority
These variables are the same for every spawning civ, and they all make sense, too. And this is a one-time deal; either the city flips or it doesn't. Obviously new Civs need a capitol, and MAYBE another city or two, but that's it. The hard part is juggling all of the factors before-hand, rather than "spawn camping" a new civ. Arabia might be an exception in that it will start with a massive military and religious presence (missionaries); America will still have some guns, and quite a lot of British or other cities nearby will flip; they can take the rest. The AI shouldn't be that defended, anyway; otherwise the barbs need more tweaking.
Did anybody actually read all that? Kudos and thanks!
I'll step down from my high horse, now.
SilverKnight
, I was very pleased to see that i had settled Constantinopolis.
Perfect compromise, sounds like. I'll test it as soon as I get back from job-hunting this afternoon, and as... what the hey, Rome! 
