548 THE AMERICAN JOURNAL OF SOCIOLOGY
a complex whole, made up of parts ; it is a social group formed from secondary groups. Its total function, however, is not distributed among these parts. And the parts or secondary groups themselves may or may not have a definite localization in the territory occupied by the group as a whole. When they are localized and not specialized we have the kind of city which we have termed undifferentiated (indifferenciee) . When they are localized and specialized, there is what we may call a differenti- ated {differ enciee) city, thus conferring upon that word a special and definite sense which refers exclusively to the internal functioning of the urban organism.
Thus, in its morphology as in its functioning, the city in its simple and primitive form appears to be a community comparable to the rural milieu which surrounds it. It differs only because of a certain closing in or contraction which results in a greater density of men and things in the urban region. The city then by no means implies, as has often been said, a high development of commercial functions and relations. For it to come into existence it is necessary, but also sufficient, that, for any cause whatever, a complex community, i. e., a community composed of secondary groups, should be compelled to contract, to reduce the territory which it occupies and to confine itself to a narrower region. For this reason it is possible for cities to originate in communities as yet little developed, where war is almost constant and where as a consequence the social groups could not exist in a scattered condi- tion. It is under such conditions that most of the cities among the aborigines of Africa and of America have arisen. Thus war has played the same role in the formation of urban civilizations that commerce comes to play in its turn. Operations of exchange have succeeded in this respect merely in developing and trans- forming the beginnings which had been made before. This shows why the commercial centers have always grown up around previously formed military centers. The original causes of the city then are not industrial. But only with the growth of indus- trial relations can the most advanced types of the city appear.
