The free cities developed under the shelter of communal liberties, and in them art and invention flourished, producing the beauty of Raphael, the vigor of Michaelangelo, the poetry of Dante, and “the discoveries which have been made by modern science,--the compass, the clock, the watch, printing, gunpowder, the maritime discoveries, the law of gravitation.”[XXI-4] Then, there came the modern State formed by a triple alliance of the military chief, the Roman judge, and the priest. The industrial revolution and the rise of capitalism furthered the interests of the military-legal-priestly triumvirate. When the State and Church were separated, the money baron took the place of the priest in the triumvirate. With the overthrow of militarism the power of the triumvirate is broken, and the old communal co-operative feelings of man again begin to express themselves. Kropotkin led the way in defining the law of co-operative individualism. He urged decentralization in social control, and attacked monopolies of all types, public as well as private. Although he exaggerated the rôle of mutual aid in primitive society, considering it the main social factor, he nevertheless rendered a valuable service in giving the world a vigorous presentation of a significant concept. The social process was analyzed in terms of both conflict and co-operation by Gustav Ratzenhofer (1842–1904). It is characterized by a continuous reappearance of the phenomena of individualization of structures already extant.[XXI-5] Both differentiation and socialization arise out of the operation of human interests. Both are implicit in the nature of man. Certain human interests lead to individualization and some to communitization. At this point we encounter Ratzenhofer’s theory of force. Force and interest are made the two primordial principles. These two factors work together in order to secure for the individual the largest possible degree of self development. The struggle of pre-primitive men against the harsh phases of nature established a pre-primitive sociality. Struggle has always led to co-operation in the interests of preservation. Similarly, war leads to co-operation. In primitive society institutions arose in response to community needs. Among barbarians the increase in numbers produced an increasing emphasis upon conflict, which was expressed in robberies, wars, and enslavements. Warfare led to the formation of classes and class conflicts. Class interests, as distinguished from individual interests, then began to secure definition. With the rise of capitalism, the interests of capital were asserted; and at once the interests of labor, in apposition, assumed tangible expression. A stage, however, of stable social conditions is coming, in which the whole world will be organized on the basis of a single system of economic and non-competing production and of free international exchange.[XXI-6]