What are the ways that trade can occur between civilizations?
There are three ways you can trade goods (specifically luxury or strategic resources – not things like world maps, right of passages, etc.) with an AI: by land, sea, or air. The land option requires you have a road path from your capital to the AI’s capital, whether it goes directly to them (e.g. you are neighbors), or it travels through another civilization (who you are both at peace with). However, a land route like this can also be pillaged if there is only one road between the two of you and an enemy unit pillages the tile, so it’s best to have multiple trade routes. Sea trade routes require each civilization trading to have a city with a harbor (and then that city connected to the capital city). Then, goods from the capital go to the harbor, which go to the AI’s harbor, then to their capital! You can only trade over coast at the beginning of the game, though, but you can later trade over sea tiles when you research Astronomy, and then all water tiles including ocean when you disco
