There is no more significant commentary on the growth of international law, both in precision and in comprehensiveness, than an estimate of the relative authority of the name of Vattel in the world of international relations a century ago and in that of today. A century ago not even the name of Grotius himself was more potent in its influence upon questions relating to international law than that of Vattel. Vattel's treatise on the law of nations was quoted by judicial tribunals, in speeches before legislative assemblies, and in the decrees and correspondence of executive officials. It was the manual of the student, the reference work of the statesman, and the text from which the political philosopher drew inspiration. Publicists considered it sufficient to cite the authority of Vattel to justify and give conclusiveness and force to statements as to the proper conduct of a state in its international relations.At the present day the name and treatise of Vattel have both passed into the remoter field of the history of international law. It is safe to say that in no modern controversy over the existence and force of an alleged rule of international law would publicists seek to strengthen the position taken by them by quoting the authority of Vattel. As an exposition of the law of nations at a given period of its growth, the work can, it is true, lose nothing of its value, but in saying that it has thus won its place irrevocably among the classics of international law, we are merely repeating that it has lost its value as a treatise on the law of the present day.
Emmanuelle Jouannet. The Liberal-Welfarist Law of Nations: A History of International Law