The campaigns of 1864-71 which led to the union of Germany under Prussia's leadership cannot be described here. (See SCHLES WIG-HOLSTEIN QUESTION ; GERMANY ; AUSTRIA ; FRANCO-GERMAN WAR.) The acquisition of Hanover, Kurhesse, Nassau and Frank furt-am-Main after the war of 1866, gave Prussian territory a wholly new aspect. Its eastern and western halves, which up to this date had been separated by these districts, were now linked up into a single great North German State, containing nearly two-thirds of the total population of Germany (in 1914, 40,000,000 out of a total population of 65,000,00o). The great problem which arose for Prussia out of the unification of Germany was. how far the independence and individuality of the Prussian State were to be retained within the new empire. Bismarck attempted to solve this problem by uniting the offices of adminis trative head of the empire (Reichskanzler) and Prussian minister president in one person, just as the dignity of the German em peror was indissolubly united with that of king of Prussia. At tempts to divide the two offices having proved impracticable, this arrangement lasted until 1918.
The alliance concluded by Bismarck with the Liberals at the time of the foundation of the empire had important effects. The Local Government Act of 1872 increased the autonomy of the rural districts, thus linking up with the traditions of the age of Freiherr von Stein. The so-called Kulturkampf—the struggle against the Catholic Church which was waged in the '7os—was also in accord with Liberal ideas. It ended, however, finally, with the State restoring to the Church its control over the pre liminary training of the clergy, and retaining only a right of veto over appointments to ecclesiastical posts.
During the short reign of Frederick III. (March–June 1888) and under William II., the situation remained in essence un changed. The new Rural Districts Act (Landgemeindeordnung) of 1892 carried existing institutions a step further. The fiscal reform carried through about the same time by von Miguel made self-assessment the basis of taxation, and provided relief for the poorer classes and heavier contributions from large incomes. On the other hand, the repeated efforts to introduce a radical reform of the franchise for the second chamber and abolish the three-class franchise, led to no result. After the revolution of 1918 Prussia adopted the republican form of State and general and secret franchise. The struggles of the latest period turned in the main round the remodelling of the bureaucracy, in which the new regime wanted to replace the old conservative element by persons more in sympathy with the democratic and socialist views of the new majority. The relation between Prussia and the Reich now took on an essentially new form, the personal union which had hitherto been customary in the higher posts having ceased to exist. Prussia was not given a special president of State; but the Prussian minister-president was separate alto gether from the chancellor of the Reich. The friction which con sequently arose between the greatest German State and the Gov ernment of the Reich was a cause of lasting difficulties, and the question arose, whether it would not be better to subdivide Prussia into a number of smaller states. It seemed very doubtful, however, whether this expedient would prove at all successful. (See also GERMANY : History.) Period. J. Voigt, Geschichte Preussens bis zum Untergang der Herrschaft des Deutschen Ordens (9 vols.; 1827 39) ; H. von Treitschke, Das deutsche Ordensland Preussen (in his Historische and politische Aufsiitze (1865) ; F. Holtze, Geschichte der Mark Brandenburg (1912).
Later Period. L. von Ranke, Zwolf Bucher Preussischer Geschichte (Works), vols. 25-27, 1865-90) ; J. G. Droysen, Geschichte der preussischen Politik bis 1756 (2nd ed. 14 vols., 1868) ; E. Berner, Geschichte des Preussischen Staates (2nd ed., 1896) ; G. Schmoller, Umrisse and Untersuchungen zur V erfassungs-, Verwaltungs- and Wirt schaftsgeschichte, besonders des preussischen Staates (1898), and Preussische Verfassungs-, Verwaltungs- and Finanzgeschichte (1921) ; H. Prutz, Preussische Geschichte (4 vols., 1899-1902) ; A. Waddington, Histoire de Prusse (to 1688, 1911) ; R. Koser, Geschichte der branden burgisch-preussischen Politik, vol. i., to 1648 (1915) ; 0. Hintze, Die Hohenzollern and ihr Werk (5th ed., 1916). (E. BRA.)