Flag of the German Empire

The black-white-red flag (Schwarz-Weiß-Rot), also known as the flag of the German Empire, the Imperial Flag (Kaiserflagge) or the Empire Flag (Reichsflagge), is a combination of the flag of Prussia and the flags of the Holy Roman Empire and the Hanseatic League. Starting as the national flag of the North German Confederation, it would go on to be commonly used officially and unofficially under the nation-state of the German Reich, which existed from 1871 to 1945.

Source: Wikipedia — Flag of the German Empire (CC BY-SA 4.0)