I've been looking for a freeciv setting that would allow me to choose between razing a city when capturing it and keeping the city. Couldn't find it in the options dialog. I'm asking here to make sure I didn't overlook it.
For now, if I want a city destroyed, I'm using a wave of "Poison city" spy attacks which reduces the population to 1. Then the city gets destroyed when I capture it.
Another way to decrease the population to 1 is using nukes, but this is expensive and has a very negative impact on the ecology, so it doesn't suit me.
Best Answer
According to the Freeciv wiki cities are only destroyed while at level 1. The forums also seem weary of this topic, which implies it is one of those oft-requested, never-to-be implemented features.
This leaves the conclusion that it is not possible to do so.