Hello again! Now much going on here right so now so maybe a good time to start a discussion ... what if trade routes to foreign cities were only possible with open borders once your trade partner has civil service? Right now, you can trade with anyone unless you are at war, even against their will. Open borders do not affect trade. This seems strange? With the proposed change, open border become more important. Up to classical era everything works as before, borders are open by default. Once explicit open borders become available, the default must logically be closed borders, preventing trade. I don't know if this has been discussed before, what's your opinion? Is this worth exploring further? There will be second-order effects for diplomacy, religion etc which need to be considered.