Though Grand Duke Frederick William openly rejected the Prussian annexation of the Kingdom of Hanover, the Prussian Army had been aided by soldiers from Mecklenburg-Strelitz in the Austro-Prussian War of 1866. Thereupon, the Grand Duchy joined the North German Confederation and the reconstituted "Zollverein". Also in the Franco-Prussian War of 1870/71, the Kingdom of Prussia received valuable assistance from Mecklenburg-Strelitz. In 1871 both Mecklenburg-Schwerin and Mecklenburg-Strelitz became States of the German Empire. Mecklenburg-Strelitz returned one member to the Bundesrat chamber of states. However, the Grand Duke was still styled Prince of the Wends and the internal government of Mecklenburg-Strelitz remained unmodernized. Mocked by Chancellor Otto von Bismarck as a safe haven in the face of threatening apocalypse "as everything there happens 50 years later", the Grand Duchy had always been a government of feudal character. The Grand Dukes exercised absolute power through their ministers, with an antiquated type of diet representing social classes. It met for a short session each year, and at other times was represented by a committee consisting of the proprietors of knights' estates (), known as the "Ritterschaft", and of the "Landschaft", which was composed of burgomasters of selected towns. There was now a renewal of agitation for a more democratic constitution, and the German Reichstag gave some countenance to this movement. In 1904 Adolphus Frederick V, a son of Grand Duke Frederick William and his wife Princess Augusta of Cambridge, daughter of Prince Adolphus, became grand duke of Mecklenburg-Strelitz. In 1907, the grand duke promised a constitution to the duchy's subjects, but this was met with opposition from the nobility. The Mecklenburg-Strelitz dynasty ended just prior to the loss of the monarchy in developments associated with World War I. At that time, there existed only two surviving recognized male dynasts of Strelitz, the young Grand Duke Adolphus Frederick VI, and his cousin Charles Michael, who was in Russian service, being a son of Grand Duchess Catherine Mikhailovna. In 1914, before the proclamation of war between Germany and Russia, Duke Charles Michael renounced his Mecklenburgish citizenship. On 23 February 1918, Grand Duke Adolf Frederick VI committed suicide, leaving his cousin Charles Michael as heir to the Strelitz throne.