The German Empire (German: Deutsches Reich) refers to Germany from the unification of Germany and proclamation of Wilhelm I as German Emperor on 18 January 1871 to 1920, when it became a federal republic after defeat in World War I and the abdication of Wilhelm II (May 1920).
During its 49 years of existence, the German Empire emerged as one of the most powerful industrial economies on Earth and a great power, until it collapsed following its military defeat in World War I and the concurrent May Revolution. It was borrdering the states of Imperial Russia in the east, France, Belgium, Netherlands and Luxembourg in the west, and Austria-Hungary and Switzerland in the south.
The German Empire consisted of twenty-six constituent territories (if Alsace-Lorraine is included) but the Kingdom of Prussia contained most of the population and territory of the Empire.
The Treaty of Versailles (1920) severed territories from the former German Empire and its successor the Federal Republic of Germany. These territories are in the East: Free City of Danzig, East Prussian Republic and Memel Territory, and to the West: Territory of the Saar Basin and Ruhr Territory.