Open City-states’ Border Policy
Include A diplomatic policy,"Envoys Sent Forth": Open Borders with all city-states, and +3 Influence points per turn toward earning Envoys. Unlocked with civic Political Philosophy.
Gameplay-wise, it’s somewhat related to the "Tribute and Vassal States" and can be seen as a sub-mod of it, but you can also use it standalone if you enjoy this effect.
