As early as 1818 the great reaction against all liberal sentiments in political matters had fairly set in. The king of Prussia neglected, and finally refused, to grant the constitutional government which he had promised in the day of his adversity before the battle of Waterloo; while Austria, guided by Metternich, stamped her iron heel on everything which looked like intellectual or national independence. This memorable reaction against all progress in government, not confined to the German States but extending to Europe generally, has already been considered in previous chapters. It was the great political feature in the history of Europe for ten years after the fall of Napoleon, particularly in Austria, where hatred of all popular movements raged with exceeding bitterness, intensified by the revolutions in Spain, Italy, and Greece. The assassination of Kotzebue, the dramatic author, by a political fanatic, for his supposed complicity with the despotic schemes of the Czar, kindled popular excitement into a blazing flame, but still more fiercely incited the sovereigns of Germany to make every effort to suppress even liberty of thought. During the period, then, when ultra-conservative principles animated the united despots of the various German States, and the Diet controlled by Metternich repressed all liberal movements, little advance was made in Prussia in the way of reforms. But a great advance was made in all questions of political economy and industrial matters. Free-trade was established in the most unlimited sense between all the states and provinces of the Confederation. All restraints were removed from the navigation of rivers; new markets were opened in every direction for the productions of industry. In 1839 the Zollverein, or Customs-Union, was established, by which a uniform scale of duties was imposed in Northern Germany on all imports and exports. But no political reforms which the king had promised were effected during the life of Frederick William III. Hardenberg, who with Stein had inaugurated liberal movements, had lost his influence, although he was retained in power until he died. For the twenty years succeeding the confederation of the German States in 1820, constitutional freedom made little or no progress in Germany. The only advance made in Prussia was in 1823, when the Provincial Estates, or Diets, were established. These, however, were the mere shadow of representative government, since the Estates were convoked at irregular intervals, and had neither the power to initiate laws nor grant supplies. They could only express their opinions concerning changes in the laws pertaining to persons and property.