The topic of discussion for this Constitution Monday comes from Article I. Section 10, Clause 3: "No State shall, without the Consent of Congress, lay any Duty of tonnage [on ships]. This provision in the Constitution allowed all ports to compete equally for business unless designated otherwise by Congress.
"A duty on tonnage was a tax on the cubical capacity of a ship. It was designed to cover the cost of dredging out the harbor, building breakwaters, and putting in piling for the construction of piers. Obviously, it would be to the advantage of the federal government to assist those ports which were needed for naval operations or acted as military bases. In all other cases they were to be treated equally" (W. Cleon Skousen in The Making of America - The Substance3 and Meaning of the Constitution, p 503).
"The Framers of the Constitution had little difficulty seeing that combinations among the states, or any foreign-affairs activities undertaken by the states, were so fraught with danger to the union, that none should be allowed unless Congress consented. Comparable prohibitions had already been contained in the Articles of Confederation, but the Framers chose somewhat stronger language in the Constitution to assure national supremacy in foreign affairs and in relations among the states. The provisions caused no significant debate at the Constitutional Convention…" (Michael S. Greve in The Heritage Guide to the Constitution, p. 178).