In 1866 the grand duchy joined the North German Confederation and the Zollverein, and came under the influence of the Kingdom of Prussia, which in the Austro-Prussian War with the Empire of Austria had been aided by soldiers from Mecklenburg-Strelitz. Also in the Franco-Prussian War the Kingdom of Prussia received valuable assistance from Mecklenburg-Strelitz. In 1871 the grand duchy became a state of the German Empire. Mecklenburg-Strelitz returned one member to the Reichstag. However, the grand duke was still styled Prince of the Wends, and the internal government of the duchy remained unmodernized. 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 duchy had always been a government of feudal character, the grand dukes exercising 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 (Rittergüter), known as the Ritterschaft, and of the Landschaft, which was composed of burgomasters of selected towns. Mecklenburg-Strelitz returned one member to the Reichstag. The grand duke was still styled Prince of the Wends.
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. Being in Russia, however, Charles Michael did not assume the throne, and in 1918 he wrote to Grand Duke Frederick Francis IV of Mecklenburg-Schwerin, who was acting as regent in Strelitz, stating that he wished to renounce his rights of succession to Strelitz, though the letter was only received by Frederick Francis in 1919 after the end of the German monarchies, so the issue of succession could not be resolved at the time.
The House of Mecklenburg-Strelitz survives to this day, descending from Duke George, the morganatic son of Duke George Alexander with Countess Natalia Carlow and nephew of Duke Charles Michael, who adopted him in 1928. George subsequently assumed the title "Duke of Mecklenburg" (Serene Highness) which was acknowledged by Grand Duke Frederick Francis IV of Mecklenburg-Schwerin. He was later given the style of "Highness" by the House of Mecklenburg-Schwerin. George's grandson Borwin is the present head of the House of Mecklenburg-Strelitz.
The county of Mecklenburg in the U.S. state of North Carolina, which includes the city of Charlotte, is named after the duchy.