Few words have been used with more different meanings than the word “law.” “International law” has likewise had many diverse definitions. The term, international law, is here used to cover the rules and principles which are generally observed in the relations among states. As laws in general become serviceable as their observance becomes regular, so international law becomes serviceable as its rules and principles are generally followed.

The modernization of international law would imply the adaptation of international law to modern conditions. Conditions have changed since the old days when “strange air made a man unfree;” when all foreigners were enemies; when emigration was prohibited lest all man-power of a state might leave and there might be no available material for an army; or when such principles generally prevailed as that of Machiavelli, which he enunciates in the following words: “that whoever is the occasion of another's advancement is the cause of his own diminution” (Chap. 3).

The development of the family of nations idea, and its extension from the Christian European states to other so-called Christian states, and later to states having a recognized political standing, regardless of religious or ethnic bases, shows the enlarging aspects of international relationship. In order that this relationship might continue, it was necessary that principles generally recognized by those having control of political affairs as worthy of their support should underlie these relationships.