The cost of operations, civil service employees, and the fact the shipments were handled at those points, all bring dollars to the area (free capital). Importer will get his money back for the tarriffs paid by passing that it on to the customer. Further shipments, i.e. to the South, would incure more cost plus, if it was in high demand, and their was a monopoly in those foreign imports, the cost again would go up.
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David Upton