The slow weakening of the Tokugawa Shogunate was due to causes not unlike those which had brought about the decline of previous regencies: the race degenerated during that long period of peace which its rule had inaugurated; the strong builders were succeeded by feebler and feebler men. Nevertheless the machinery of administration, astutely devised by Iyeyasu, and further perfected by Iyemitsu, worked so well that the enemies of the Shogunate could find no opportunity for a successful attack until foreign aggression unexpectedly came to their aid. The most dangerous enemies of the government were the great clans of Satsuma and Choshu. Iyeyasu had not ventured to weaken them beyond a certain point: the risks of the undertaking would have been great; and, on the other hand, the alliance of those clans was for the time being a matter of vast political importance. He only took measures to preserve a safe balance of power, placing between those formidable allies new lordships in whose rulers he could put trust,--a trust based first upon interest, secondly upon kinship. But he always felt that danger to the Shogunate [368] might come from Satsuma and Choshu; and he left to his successors careful instructions about the policy to be followed in dealing with such possible enemies. He felt that his work was not perfect,--that certain outlying blocks of the structure had not been properly clamped to the rest. He could not do more in the direction of consolidation, simply because the material of society had not yet sufficiently evolved, had not yet become plastic enough, to permit of perfect and permanent cohesion. In order to effect that, it would have been necessary to dissolve the clans. But Iyeyasu did all that human foresight could have safely attempted under the circumstances; and no one was more keenly conscious than himself of the weak points in his wonderful organization.