(_c_) Treaties and state papers may agree as to rules which shall be held as binding upon the parties to the treaty or paper. The Declaration of Paris, 1856, agreed as to certain principles and rules of maritime international law, which should be held as binding the signatory powers or those later agreeing to its provisions. This Declaration may be held as generally binding. The United States, by Proclamation of April 26, 1898, announced its adherence to the principles of the Declaration, and during the same year Spain acquiesced in its principles.
(_d_) Most treaties and state papers, however, deal with matters of interstate politics, and are not in any sense sources of international law. They are in most cases little more than interstate compacts.
During the seventeenth and the first half of the eighteenth century, the writings of the great publicists were regarded as the highest source of authority upon matters now in the domain of international law. These writings not only laid down the principles which should govern cases similar to those which had arisen, but from the broad basis given the law of nations, deduced the principles for such cases as might arise. This latter method was especially common among the early writers, such as Victoria and Suarez in the sixteenth century. The philosophical school, from Grotius to the middle of the eighteenth century, continued to propound the principles which should govern in supposed cases, should they ever actually arise. Statesmen looked to these treatises as authoritative sources. The prolific Moser, in the middle of the eighteenth century, made the historical method more prominent by giving less attention to the natural law, and by founding his system on usage and treaties. Bynkershoek (1673-1763) had anticipated him in this method in special lines, but Moser extended the system and made it most ample. Succeeding writers mingled the two systems, inclining to the one or the other. In the early days of the modern period, the writers upon the law of nations, outlined the course which states should pursue in their relations to one another. In the later days of the modern period, the writers upon the law of nations, while sometimes discussing problems before they arise, in general attempt to expound the rules and principles which have entered already into interstate action. The works of the text writers, from Grotius to the present, must be regarded as sources of highest value.