The order operated upon the vessels and merchandise of all nations, whether belonging to citizens of the United States or to foreigners, arriving in any of the ports in Mexico in our military occupation. The contributions levied were a tax upon Mexican citizens, who were the consumers of the merchandise imported. But for the permit or license granted by the order all vessels and merchandise belonging to citizens of the United States were necessarily excluded from all commerce with Mexico from the commencement of the war. The coasts and ports of Mexico were ordered to be placed under blockade on the day Congress declared the war to exist, and by the laws of nations the blockade applied to the vessels of the United States as well as to the vessels of all other nations. Had no blockade been declared, or had any of our merchant vessels entered any of the ports of Mexico not blockaded, they would have been liable to be seized and condemned as lawful prize by the Mexican authorities. When the order was issued, it operated as a privilege to the vessels of the United States as well as to those of foreign countries to enter the ports held by our arms upon prescribed terms and conditions. It was altogether optional with citizens of the United States and foreigners to avail themselves of the privileges granted upon the terms prescribed. Citizens of the United States and foreigners have availed themselves of these privileges. No principle is better established than that a nation at war has the right of shifting the burden off itself and imposing it on the enemy by exacting military contributions. The mode of making such exactions must be left to the discretion of the conqueror, but it should be exercised in a manner conformable to the rules of civilized warfare. The right to levy these contributions is essential to the successful prosecution of war in an enemy's country, and the practice of nations has been in accordance with this principle. It is as clearly necessary as the right to fight battles, and its exercise is often essential to the subsistence of the army. Entertaining no doubt that the military right to exclude commerce altogether from the ports of the enemy in our military occupation included the minor right of admitting it under prescribed conditions, it became an important question at the date of the order whether there should be a discrimination between vessels and cargoes belonging to citizens of the United States and vessels and cargoes belonging to neutral nations.