Cutiestar: If you have control over cultural flips, tell me your secret
please! The strategies you, Endureth, et.al. have suggested so far
do not work, so you must be holding out!

They probably help, but they don't
prevent flipping. The only thing that does is the utter elimination of the enemy.
Two flips per game are too much, when there is no excuse for them (by which I mean well-garrisoned, rush-built up cities that are on a continent far away from the enemy's last remaining city, when I am producing ~1000 times as much culture per turn as his primitive outpost.
The "real world" comparisons you draw are inacurate. Latvia declared independance from a failing empire, and the USSR splintered more-or-less voluntarily. Or do you mean their assimilation
into the USSR? That would be similar to a strong Civ in the game assimilating a weak one - but what I have a problem with is weak civs assimilating strong ones! That's what makes me fume - and what makes the game less fun to play.
I don't believe that the situations we are complaining about have ever happened in history. Empires lose control of territories when they are on the decline, and when their military is stretched too thin. Did any cities in China (with their overwhelming culture) flip back to the Chinese while the Mongols were still on the march? If they had, what do you suppose the Khan's response would have been?
If having your modern armies defeated by unarmed civilians who have no reason to rise up doesn't frustrate you, more power to you! I laud your patience. Just recognise that you are in the minority!
I love the idea of cultural flipping. I hate
this aspect of the way it works in Civ III though.