This will depend on how the trade mechanics will work. If theres no trade between different markets than the existence of a tariff mechanic indeed kinda loose its point. I really hope thats not the case.
I'm also very worried about the "trade routes" concept and what it will reflect.
The dev diary about the trade markets and its mechanics its the one i look forward the most and it will be the one that tip the scales for my interest in this game.
A "market" doesn't necessarily mean a European Union like free trade zone and neither it should, so tariffs wouldn't and shouldn't loose it's point.
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