The gentry group, with the gradual development for several centuries, had evolved into the class of great clans in the Wei and Jin Dynasties. Together with the ruthless struggle for political power, the class of great clans became much stronger and developed steadily. At the beginning of the Western Jin Dynasty, most generals and ministers were from the great clans, who were either the high officials of the Wei Dynasty or the descendants of them. Although it seemed to be paradoxical, class solidification and dynastic replacement coexisted in medieval China. As the means of dynastic replacement with the minimum cost, the crown abdication greatly conformed to the aristocratic interests and gradually became the political spirit that were widely accepted by the gentry class. The substitution pattern of imperial power was closely related to the dominant social strata. The steady development of the great clans, the ripe theory of crown abdication, and the practice of different patterns of abdication-these three factors closely worked together so as to open the curtain of medieval aristocratic society.