I remember reading in Sullas walkthrough before the game came out that he returned a city to the control of the civ that originally controlled it, and it was an option when he captured it. In my last game I'd finished securing control of my section of the world and the resources I required, and was getting bored of just building. The Greeks on the other side of the planet had spent the entire game building up huge armies and slowly conquering the Germans and Americans to their south. I restationed most of my military over to America and started taking the ex American and German cities from that base, but I never had the option to return control to the original country - even in a city that had 85% German culture. I ended up giving one of the cities to the Americans by going into diplomacy and giving it as a gift, but I wanted to be doing proper liberation of cities, so I ended up keeping the rest for myself. I guess there must be some type of time limit on it? Has anyone else had the option to return control to the original builder of the city?