The German Empire, also referred to as Imperial Germany, the Second Reich, or simply Germany, was the period of the German Reich from the unification of Germany in 1871 until the November Revolution in 1918, when Germany changed its form of government to a republic. The German Empire consisted of 25 states, each with its own nobility: four constituent kingdoms, six grand duchies, five duchies, seven principalities, three free Hanseatic cities, and one imperial territory. While Prussia was only one of the four kingdoms in the realm, it contained about two-thirds of the Empire's population and territory, and Prussian dominance was also constitutionally established, since the King of Prussia was also the German Emperor.