There was little scope for an international law in the period of ancient and medieval empires, and its modern beginnings coincide, therefore, with the rise of national states after the Middle Ages. Rules of maritime intercourse and rules respecting diplomatic agents (see diplomatic service) soon came into existence. At the beginning of the 17th cent., the great multitude of small independent states, which were finding international lawlessness intolerable, prepared the way for the favorable reception given to the De jure belli ac pacis [concerning the law of war and peace] (1625) of Hugo Grotius, the first comprehensive formulation of international law.