blackheart
unenlightened
I've never used this tactic personally, but I have heard of success stories from it. It is basically build a city very close to the capital that will probably only utilize one tile and not have any improvements. We then use the "slave" city to trade to the AI for tech. Then a few turns later it flips back to us because of the overwhelming culture of our capital. So, tech gained, no city lost, win win for everyone
. I know it sounds a bit unethical, but just a suggestion.
