Apparently to offset the failure of the tea and coffee tax, Walker's active brain produced another scheme, designed not only to bring in revenue and reassure the capitalists, but also to please the shipping men of the United States and neutral countries. This was to open the Mexican ports controlled by us, and permit merchandise to enter there under a moderate scale of duties. During March, 1847, assisted by Senator Benton and the attorney general, Polk satisfied himself that under his powers as commander-in-chief he could impose and collect the duties as military contributions, for by the right of conquest he could either exclude commerce or admit it on his own terms, and contributions were legitimate under the laws of war. Said Vattel, "A nation [at war] on every opportunity lays its hands on the enemy's goods, appropriates them to itself, and thereby, besides weakening the adversary, strengthens itself, and at least in part, procures an indemnification, an equivalent, either for the very cause of the war, or for the expences and losses resulting from it"; and a low scale of duties was an extremely mild application of this principle.[33.16] Moreover, it was quite as legitimate under our Constitution also, though not expressly mentioned, as to blockade or bombard Vera Cruz, respecting which the organic law was equally silent. Indeed, to have left the ports wide open or allowed the high Mexican tariff to remain in force would, in addition to being harmful to us, have required as great an exercise of authority. Finally, Scott and some of our naval commanders, moved by the evident proprieties of the situation, fixed duties and used the proceeds at their discretion, and it was manifestly better to arrange the business in a uniform, well-considered manner.[33.16] It might have been expected that substantially either our own or the Mexican tariff would be applied, but neither would have answered. Mexican imports were very different from ours; specific, not _ad valorem_, duties had been customary there; and competent appraisers could not be found. On the other hand the unreasonable Mexican duties, besides preventing commerce to a large extent, encouraged fraud and smuggling. In March, 1847, therefore, a special tariff was prepared by Walker, lowering the Mexican duties on imports more than one half, and substituting for all port dues and charges a uniform tax of one dollar per ton; and on March 31 Polk ordered the system to be put in force. Mexico retorted that goods paying the American duties--especially goods prohibited by her laws--would be confiscated, and this attitude caused some uneasiness in France; but it seemed fairly evident that the United States would protect neutrals accepting our policy, and not only the foreign merchants in Mexico but the neutral governments felt highly pleased with our course.[33.17]