If the states have been loyal to the empire, the imperial government has also respected the constitutional privileges of the states. The harmonious working of the constitution depends on the union of policy between the empire and Prussia, for it is the power of Prussia which gives strength to the empire. This was practically secured by the fact that the emperor, who is king of Prussia, appoints the chancellor, and the chancellor is generally president of the Prussian ministry as well as minister of foreign affairs--in his person the government of the two is identified. For twenty years the double office was held by Bismarck, who, supported as he was by the absolute confidence of the emperor, and also of the allied princes, held a position greater than that ever attained by any subject in modern Europe since the time of Richelieu. For ten months in 1873 he, indeed, resigned the office of minister-president to Roon; and in the same way Caprivi, during the years 1893-1894, held the chancellorship alone; but in neither case was the experiment successful, and Hohenlohe and Bülow adhered to the older plan. So important is the practical co-operation of the imperial administration and the Prussian government, that it has become customary to appoint to seats in the Prussian ministry the more important of the secretaries of state who administer imperial affairs under the chancellor. Delbrück, head of the imperial chancery, had held this position since 1868; in 1877 Bülow, secretary of state for foreign affairs, was appointed Prussian minister, and this has become the ordinary practice. One result of this is to diminish the control which the Prussian parliament is able to maintain over the Prussian ministry.