I'm in a war with two countries right now, and I've captured and kept a city from each. I have built culture-generating improvements in each city, and when I zoom to the cities, they each show that I am generating culture each turn. But their cultural influence is not expanding, and both have a cultural value of zero, though they have been generating five culture per turn for some time. Is this a glitch, or is it because I took the cities from another country? If it's because I captured them, is there any way to get the influence to expand without signing peace treaties?