Paris, Declaration of, 1856, agreement concerning the rules of maritime warfare, issued at the Congress of Paris. It was the first major attempt to codify the international law of the sea. Conflicting methods used in dealing with property at sea had demonstrated the need for uniformity, while the respect paid to neutral rights in the Crimean War indicated that common principles of action would be accepted by the great powers. Four principles were enunciated by the declaration: privateering would no longer be considered legal; a neutral flag would protect the goods of an enemy, except for contraband of war; neutral goods, with the exception of contraband of war, would not be liable to capture when under the enemy's flag; a blockade would be binding only if it prevented access to the coast of the enemy. At first the United States refused to accept the declaration, claiming that privateers were necessary if a nation did not have a strong navy. However, the United States accepted the declaration during the Civil War and the Spanish-American War. At the beginning of World War I prize courts recognized the declaration, but submarine warfare and extensive lists of contraband negated its principles. Part of its aims were restated in 1909 in the Declaration of London, but technological advances made many of its provisions inapplicable in 20th-century warfare.