Got a few questions:
1. How do carriers work? I don't see where they are in the tech trees, nor any information on them.
2. How in god's name do you get a treaty beyond an exploration treaty with another race? The only treaty the AI has available is an exploration treaty, regardless of standings, techs, or anything else in my games. Either it's really buggy or I don't know what I"m doing. In a related note how would you know what treaties are in effect?
2. I've yet to see anything other than that on an AI side. I can have researched many other treaties, and we can be very Close, but I still don't see much. I can offer them plenty of the other treaties - Alliance, for one. If they're prepared to ally with me, why can't I ask for the Free Trade treaty?
To see which treaties are in effect, in the Diplomacy screen there should be a button. It shows all trades with lasting effect.