The law of nationality, which determines the relation borne by private individuals to sovereign states, is a distinct branch of public law. Being necessarily somewhat technical and detailed in its provisions, it does not ordinarily attract popular interest and attention in times of peace. However, when war breaks out, the question of nationality is seen to be one of vital importance to the state. In times of peace the population of a country presents an appearance of uniformity, and citizens and aliens mingle freely, carrying on the ordinary business of life with each other, apparently regardless of the question of allegiance. Especially has this been so in modern times, with their extensive intercourse between nations and liberal laws governing the rights of aliens. But, nevertheless, when a country is cast into the crucible of war, the component parts of its population are quickly separated into citizens or subjects, allies, alien enemies and neutrals. For some years the theory has been growing that divisions of nationality are being obliterated and replaced by economic and class divisions. The great war now being waged has proven that, whether or not the change mentioned is in a process of development, it has not yet reached the stage where it effectively controls the relation between separate countries. Divisions of nationality are still predominant.