I have 2 colonies that have declared independence (from United Earth and Zolarg). How do I get them to trade with each other?
United Earth has the transmission hub, and Zolarg have the deep space transceiver. Select one of them and use "communications." Input the chater code of the colony you want to trade with and send a message. Go to the other colony and reply to the message with a gift. You can then reply to the gift with anogher gift if you want.
You can also send a diplomatic mission from one to the other to give you a place to send gifts.