"Connected" effect + "CityState", "CapitalConnected" requirement
One of the core parts of HRM879656. The effect and the req are added in a bundle since they have no sense separately. After the capitals are identified (A question: we use here capitals or governmental centers?), the effect is run recursively for the player's cities to see if they are directly (by effect) or indirectly (through other player's cities) connected to some of the capitals, and a flag for each city is set that may be used in the requirement. The flag is updated within the turn only if either city buildings are changed or the city changes hands.
Reply To ihnatus
(A question: we use here capitals or governmental centers?)
There's actually three options: primary capital / all capitals / government centers. The City State should just be named accordingly (with the possibility to add the others later, if needed)