Couerdelion, one of the patches to Vanilla in Mercantilism also removed the ability for foreigners to establish a trade route with your cities when you ran Mercantilism.
Athough, if the only reason your running Merchantilism is to keep foreign cities from trading with you; simply closing the borders would also work.
Athough, if the only reason your running Merchantilism is to keep foreign cities from trading with you; simply closing the borders would also work.
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