"It was the desire for freedom of commerce among the states which inspired this provision as to interstate commerce in the Constitution, and all the early cases so indicate.

In fact it will be found that, within the conception of the fathers, the control which they gave over interstate commerce was intended to cover only coastwise shipping from the port of one state to the port of another state.

But there is an abundance of evidence found in the acts of the Constitutional convention, and in the construction of the Constitution by the early Presidents, to show that it was not the intent of the framers of the Constitution, under the power to regulate interstate commerce, to clothe Congress with the power to prohibit commerce. Edmund Randolph, who presented to the Constitutional Convention the Virginia plan, while Attorney-General under the administration of Washington, gave his opinion to Washington, February 12, 1791, on the extent of the power in Congress to regulate commerce, saying that its extent was ‘little more than to establish the forms of commercial intercourse between the states, and to keep the prohibitions which the Constitution imposed upon that intercourse undiminished in their operation; that is, to prevent taxes on imports or exports, preference to one port over another by any regulation of commerce or revenue, and duties upon the entering or clearing of the vessels of one state in the ports of another.’"

James Madison, Preface to Debates in the Federal Convention:
"The want of authy. in Congs. to regulate Commerce had produced in Foreign nations particularly G. B. a monopolizing policy injurious to the trade of the U. S. and destructive to their navigation; the imbecility and anticipated dissolution of the Confederacy extinguishg. all apprehensions of a Countervailing policy on the part of the U. States.

The same want of a general power over Commerce led to an exercise of this power separately, by the States, wch not only proved abortive, but engendered rival, conflicting and angry regulations. Besides the vain attempts to supply their respective treasuries by imposts, which turned their commerce into the neighbouring ports, and to co-erce a relaxation of the British monopoly of the W. Indn. navigation, which was attemted by Virga. the States having ports for foreign commerce, taxed & irritated the adjoining States, trading thro' them, as N. Y. Pena. Virga. & S–Carolina. Some of the States, as Connecticut, taxed imports as from Massts higher than imports even from G. B. of wch Massts. complained to Virga. and doubtless to other States. In sundry instances of as N. Y. N. J. Pa. & Maryd. the navigation laws treated the Citizens of other States as aliens."

Mr. Clymer. "The diversity of commercial interests, of necessity creates difficulties, which ought not to be increased by unnecessary restrictions. The Northern & middle States will be ruined, if not enabled to defend themselves against foreign regulations."

James Madison Federalist No 42:
"A very material object of this power was the relief of the States which import and export through other States, from the improper contributions levied on them by the latter. Were these at liberty to regulate the trade between State and State, it must be foreseen that ways would be found out, to load the articles of import and export, during the passage through their jurisdiction, with duties which would fall on the makers of the latter, and the consumers of the former. We may be assured by past experience, that such a practice would be introduced by future contrivances; and both by that and a common knowledge of human affairs, that it would nourish unceasing animosities, and not improbably terminate in serious interruptions of the public tranquility. "

During the debates in the Federal [Constitutional] Convention, Oliver Ellsworth stated:

"The power of regulating trade between the States will protect them against each other. "

James Madison reiterated this point in the Convention as follows:

"[P]erhaps the best guard against an abuse of the power of the States on this subject, was the right in the General Government to regulate trade between State and State. "

If we return to first principles we find this provision was simply a free trade clause.