The most significant factor of the Emperor’s rule was that it offered a center of unity to the Teutonic tribes, consolidating them, where the Merovingian kingdoms, which also stood for the old Germanic tribal traditions, had shown complete incapacity. But under the Carolingian rule, neither the Alemanni, nor the Bavarians, nor the Saxons, could claim predominance, for the sovereign’s authority was exercised apart from all these tribal influences, and yet at the same time the characteristics of the tribe, local sentiment, and customary law, were not broken up by the central government. The Teutonic local division, the “Gau,” was no more interfered with than the Gallic “Civitas.” The power at the top of all, formed by the armed hosts of the component parts of the Empire and by the clergy, was expressed in institutions that kept the body politic together. In the assemblies, all the different nationalities took part, and acted under the guidance of the single will of a single ruler, who was kept from the capricious action of a tyrant by his firm hold on the ideal of a Christian commonwealth. The principles of the whole imperial system harmonized with popular governmental traditions, and both in their social and in their religious aspects answered to the popular conceptions of membership in a world-wide church. Charles, in his plans for the succession, looked forward to a ruling family controlling by descent a singularly heterogeneous collection of races. It is unthinkable, as an historical principle, that the traditions and customs of race and tribe could be long suppressed. Since the time of Germanic invasions they had been the most potent factor in the evolution of Western Europe; and, though they were kept in the background by the energy and character of the Emperor, it only needed a few crises to call them forth into activity. Out of the interplay of these tribal interests and racial divergencies has grown modern Europe. A further weakness in the Carolingian structure was due to the relation of the secular and the ecclesiastical authority. The grounds of conflict, even in Charles’ own time, were never far distant. The Emperor’s diplomacy and personality smoothed the acerbities away, and his attitude of compromise found ready imitators in such Popes as Hadrian I and Leo III. There would have been a different outcome if, on his visits to Rome, he had been faced by a Pope of the temperament of Nicholas I. The possible independence of the spiritual power the Emperor did little to prevent by legislation. There was no way of avoiding such disputes, and the struggles for supremacy between Empire and Papacy attained their full development in the thirteenth century.