When goods were moved in or out of a port they attracted tariffs, which were originally used for the support and maintenance of the port facilities, but over time the naval powers started using them as a method for generating income especially to fund a navy which could then protect the merchant ships. With a powerful navy and a large merchant fleet power could then be projected around the world, foreign ports would want your ships to visit to trade goods that they didn’t have and your navy could transport your armies across the oceans. https://youtu.be/nI5Ckw4CtsY
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