been able to do it a few times, but it's pretty rare, and I havne't been able to really find a rhyme or reason to it. Once I got a fairly good size city (6-8 I think) in the middle of another person's empire on another continet. Very very random and unexplained.
I have to say that propaganda is not very useful. If you want some certain city, gather your forces and go get it. Why bother waist thousands of dollars on it.
Spying is useful for me to learn the positions of the enemy forces. Once I spied that around 30 of Roman tanks were gathering at one city, so I threw a nuke, and killed them all. The most efficient nuke I ever used.