Right click on the city, then property.
It's actually a very nice editor. Strap in some way to edit save games for diplomacy (and I'm sure someone will find a way to do that sooner or later and sonner more than later) and we're set for full-scale scenario editing.
Even as things are, we have rather nice scenario editing capacity for exploring "What if" scenario - IE, what if Hitler, instead of being an evil tyran, had been replaced by a rather "foresight" guy who had realized how menacing Stalin was and started outright building alliances against him? Or what if he had decided to take on Italy instead of France, regardless of alliance?
I actually rather enjoy the notion of having more freedom (as a player) regarding diplomatic situation, and be able to rewrite history as if *I* had been in command of the situation at a specific point in time, not Hitler or whoever.