Neutral goods, with the exception of contraband of war, are not liable to capture under enemy's flag.
"4.

Blockades, in order to be binding, must be effective; that is to say, maintained by a force sufficient really to prevent access to the coast of the enemy[240]." This agreement was adopted by Austria, France, Great Britain, Prussia, Russia, Sardinia and Turkey, and it was further agreed that a general invitation to accede should be extended to all nations, but with the proviso "that the powers which shall have signed it, or which shall accede thereto, shall not in future enter into any arrangement, concerning the application of the law of neutrals in time of war, which does not rest altogether upon the four principles embodied in the said declaration[241]." In other words it must be accepted in whole, and not in part, and the powers acceding pledging themselves not to enter into any subsequent treaties or engagements on maritime law which did not stipulate observance of all four points.

Within a short time nearly all the maritime nations of the world had given official adherence to the Declaration of Paris.
But the United States refused to do so.

She had long stood in the advance guard of nations demanding respect for neutral rights.

Little by little her avowed principles of international law as regards neutrals, first scoffed at, had crept into acceptance in treaty stipulations.
Secretary of State Marcy now declared, in July, 1856, that the United States would accede to the Declaration if a fifth article were added to it protecting all private property at sea, when not contraband.