I agree with what a lot of you have said but another factor for terror I believe would be a great addition the secret police. Okrana and Cheka for example. This whould differ from gov't to gov't. For example under communism the secret police would be able to find and kill spies easier than in Republic for example. They would all have different abilities and weaknesses and be able to counter the terrorists or freedom fighters what ever you want to call them. They could increase city production by scaring them into working. When you steal a city and haven't assimulated the population it could be taken to a conentration camp, which like a colony had to be defended, and made to work. Obviously the camp would be within your culture boundries