Prussia (German:  Preußen (help·info); Latin: Borussia, Prutenia; Latvian: Prūsija; Lithuanian: Prūsija; Polish: Prusy; Old Prussian: Prūsa; Danish: Prøjsen; Russian: Пру́ссия) was a German kingdom and historic state originating out of the Duchy of Prussia and the Margraviate of Brandenburg. For centuries, the House of Hohenzollern ruled Prussia, successfully expanding its size by way of an unusually well-organized and effective army. Prussia shaped the history of Germany, with its capital in Berlin after 1451. By 1871, the smaller German city states were merged with Prussia, resulting in the creation of the German Empire. In November 1918 the royalty abdicated and the nobility lost most of its political power. Prussia was effectively abolished in 1932, and officially abolished in 1947.

The name Prussia derives from the Old Prussians. In the 13th century, "Old Prussia" was conquered by German crusaders, the Teutonic Knights. In 1308 Teutonic Knights conquered the formerly Polish region of Pomerelia with Gdańsk (Danzig). Their monastic state was mostly Germanized through immigration from central and western Germany and in the south it was Polonized by settlers from Masovia. After the Second Peace of Thorn of 1466, Prussia was split into the western Royal Prussia, a province of Poland, and the eastern part, since 1525 called Duchy of Prussia, a fief of the Crown of Poland up to 1657. The union of Brandenburg and the Duchy of Prussia in 1618 led to the proclamation of the Kingdom of Prussia in 1701.