"Finally, when your empire's Unhappiness (Civ5) Unhappiness reaches -20, given your Public Opinion is low, some of your cities may start to revolt and change their allegiance to other empires following their Preferred Ideology. The effect is as if the other empire suddenly acquired the city in question. Border cities are most likely to defect, and the civilization they go to is the one with the Preferred Ideology, whose Capital is closest to the city."
Meg is találtam a válaszomat, mindenesetre jó taktika így városokat megszerezni :D