THE doctrine pacta sunt servanda is an ancient one, universally acknowledged, but the principle upon which it rests has been the subject of much disagreement. In early times the force which international treaties were relied upon to exert was thought to have its origin in the religious atmosphere which usually surrounded their conclusion, consecrated by oaths and solemn promises. By the time of Grotius, this theory had given way to precepts of natural law. It was a "categorical imperative" that impelled the parties to recognize the moral obligation assumed in treaties. In more recent times it has been maintained that "international treaties have obligatory force only when there are norms which are above treaties, that is, norms which confer upon the treaties their legal power."1 By these "norms" we understand today the sovereign authority of the state, which is the source of the supreme law of the land. However, sovereignty in the usual acceptance of the term, while it may account for the authority to enter into treaties, is hardly adequate to furnish the basis for their binding force, since logically sovereignty is incompatible with obligation, and theoretically there would be nothing to prevent a sovereign state from releasing itself from the engagement undertaken in international treaties.
Despite the sanctity of treaties, whether based upon religious, moral, or political theory, practical measures have customarily been resorted to to insure their being carried out. One of the earliest was the taking of hostages, who served as a pledge for the fulfillment of the treaty.2 This custom is preserved today____________________