Eigenvector said:I always play totally isolationist and I've never had a problem winning a game. Now that may change as my difficulty levels increase, but so far I haven't seen any reason to open my borders.
As you increase your difficulty level, you will start needing the extra trade and ability to send in missionaries, as well as the improved relationship it gives that you'll probably need to start tech and resource trading (and also to keep them from attacking you). If you don't open borders, they'll start demanding tributes. And if you refuse those, they'll come knocking with an army and try to take it.