The right to levy contributions upon the enemy in the form of import and export duties in his ports was sanctioned by the treaty of peace with Mexico.  By that treaty both Governments recognized ... and confirmed the exercise of that right.  By its provisions “the customhouses at all the ports occupied by the forces of the United States” were, upon the exchange of ratifications, to be delivered up to the Mexican authorities, “together with all bonds and evidences of debt for duties on importations and exportations not yet fallen due;” and “all duties on imports and on exports collected at such custom-houses or elsewhere in Mexico by authority of the United States” before the ratification of the treaty by the Mexican Government were to be retained by the United States, and only the net amount of the duties collected after this period was to be “delivered to the Mexican Government.”  By its provisions also all merchandise “imported previously to the restoration of the custom-houses to the Mexican authorities” or “exported from any Mexican port whilst in the occupation of the forces of the United States” was protected from confiscation and from the payment of any import or export duties to the Mexican Government, even although the importation of such merchandise “be prohibited by the Mexican tariff.”  The treaty also provides that should the custom-houses be surrendered to the Mexican authorities in less than sixty days from the date of its signature, the rates of duty on merchandise imposed by the United States were in that event to survive the war until the end of this period; and in the meantime Mexican custom-house officers were bound to levy no other duties thereon “than the duties established by the tariff found in force at such custom-houses at the time of the restoration of the same.”  The “tariff found in force at such custom-houses,” which is recognized and sustained by this stipulation, was that established by the military order of the 31st of March, 1847, as a mode of levying and collecting military contributions from the enemy.

The right to blockade the ports and coasts of the enemy in war is no more provided for or prescribed by the Constitution than the right to levy and collect contributions from him in the form of duties or otherwise, and yet it has not been questioned that the President had the power after war had been declared by Congress to order our Navy to blockade the ports and coasts of Mexico.  The right in both cases exists under the laws of nations.  If the President can not order military contributions to be collected without an act of Congress, for the same reason he can not order a blockade; nor can he direct the enemy’s vessels to be captured on the high seas; nor can he order our military and naval officers to invade the enemy’s country, conquer, hold, and subject to our military government his cities and provinces; nor can he give to our military and naval commanders orders to perform many other acts essential to success in war.