The second method of forming great political bodies was that of _conquest with incorporation_. The conquering tribe, while annexing its neighbours, gradually admitted them to a share in the government. In this way arose the Roman empire, the largest, the most stable, and in its best days the most pacific political aggregate the world had as yet seen. Throughout the best part of Europe, its conquests succeeded in transforming the ancient predatory type of society into the modern industrial type. It effectually broke up the primeval clan-system, with its narrow ethical ideas, and arrived at the broad conception of rights and duties coextensive with Humanity. But in the method upon which Rome proceeded there was an essential element of weakness. The simple device of representation, by which political power is equally retained in all parts of the community while its exercise is delegated to a central body, was entirely unknown to the Romans. Partly for this reason, and partly because of the terrible military pressure to which the frontier was perpetually exposed, the Roman government became a despotism which gradually took on many of the vices of the Oriental type. The political weakness which resulted from this allowed Europe to be overrun by peoples organized in clans and tribes, and for some time there was a partial retrogression toward the disorder characteristic of primitive ages. The retrogression was but partial and temporary, however; the exposed frontier has been steadily pushed eastward into the heart of Asia; the industrial type of society is no longer menaced by the predatory type; the primeval clan-system has entirely disappeared as a social force; and warfare, once ubiquitous and chronic, has become local and occasional.