What does it take for a civ to become connected to the trade network?

[Strategist83]

I'm not talking about cities but the civ as a whole. I notice that sometimes I can't trade with my neighbour even though we have cities on the same coast. Why is that? What is required to be connected?

[Ijuin]

If the other civ does not have Sailing, then they can not trade along the coast. You are probably better off trying to build a road to them.

If you are talking about trading resources, only those resources that one of you has and the other does not are shown. If neither of you has a resource that the other lacks, then no resources can be traded.

If you are talking about trade routes (that generate commerce in cities), then make sure that neither you nor they are running Mercantilism, which blocks all international trade routes.

[Strategist83]

So, I have to build roads to them or provide them with sailing technology. This is what I've already been trying to do and was confused when it still didn't work.

Oh well, thank you.

[Dauphin]

Make sure that you have mapped out the coastal route, sometimes if you have uncharted tiles blocking the route there will be no trade.

Also, not directly related to your situation, you need Astronomy to trade over oceans.