The Kingdom of Prussia (German: Königreich Preußen) was a German kingdom from 1701 to 1918. From the 1871 unification of Germany to its defeat in World War I, Prussia comprised almost two-thirds of the territory of the German Empire. It took its name from the territory of Prussia, although its power base was Brandenburg.

Since 1618, the Electorate of Brandenburg and the Duchy of Prussia were ruled in personal union by the House of Hohenzollern ("Brandenburg-Prussia"). In the course of the Second Northern War, the Treaty of Labiau and the Treaty of Wehlau-Bromberg granted the Hohenzollern sovereignty in the Prussian duchy. Thus, in return for an alliance against France in the War of the Spanish Succession, Elector Frederick III crowned himself "King in Prussia" as Frederick I in 1701. Technically, no kingdoms could exist in the Holy Roman Empire except for Bohemia. However, Frederick took the line that since Prussia had never belonged to the Empire and the Hohenzollerns were fully sovereign over it, he could elevate Prussia to a kingdom. The title "King in Prussia" was adopted because they were still only electors within that portion of Prussia that was still part of the Holy Roman Empire. It was not until 1772 that the title was changed to "King of Prussia."

Frederick II (German: Friedrich II.; 24 January 1712 – 17 August 1786) was a King in Prussia (1740–1772) and a King of Prussia (1772–1786) from the Hohenzollern dynasty. In his role as a prince-elector of the Holy Roman Empire, he was also Elector of Brandenburg. He was in personal union the sovereign prince of the Principality of Neuchâtel. He became known as Frederick the Great (Friedrich der Große) and was named Der Alte Fritz ("Old Fritz").

Interested primarily in music and philosophy and not the arts of war during his youth, Frederick unsuccessfully attempted to flee from his authoritarian father, Frederick William I, with childhood friend Hans Hermann von Katte, whose execution he was forced to watch after they were captured. Upon ascending to the Prussian throne, he attacked Austria and claimed Silesia during the Silesian Wars, winning military acclaim for himself and Prussia. Near the end of his life, Frederick physically connected most of his realm by conquering Polish territories in the First Partition of Poland.