KING IN PRUSSIA

'King in Prussia' () was a title used by the Electors of Brandenburg from 1701 to 1772. Subsequently they used the title ''King of Prussia''.
The Prince-Elector of Brandenburg was a subject of the Holy Roman Emperor. In addition to his electorate which was part of the Holy Roman Empire, he also ruled the Duchy of Prussia which lay outside of the Empire. In 1701 Elector Frederick III wanted to show his greatness by adopting the title ''king''. At the time there were only three royal titles within the Empire: "King of the Germans" (a title held by the Emperor), "King of Bohemia" (often held by the Emperor as well), and "King of the Romans" (held by the Emperor's heir).
In return for Hohenzollern assistance in the War of the Spanish Succession, Emperor Leopold I allowed Frederick to crown himself "King ''in'' Prussia", not "King ''of'' Prussia"; Frederick was only an elector in his domains within the borders of the Empire, not a king. Even so, his move was controversial, and only became widely accepted after the Treaty of Utrecht in 1713. The title "King of Prussia" implied lordship over the entire Prussian region, not simply the Duchy of Prussia, and the assumption of such a title by the Hohenzollern margraves would have threatened neighboring Poland; because the province of Royal Prussia was part of the Kingdom of Poland, the Kings of Poland titled themselves ''Kings of Prussia'' until 1742.
Throughout the 18th century the power of the Kings in Prussia continued to increase. They were victorious over the Austrian Habsburg Monarchy in the three Silesian Wars, greatly increasing their power through the acquisition of Silesia. King Frederick II adopted the title ''King of Prussia'' in 1772, the same year he annexed most of Royal Prussia in the First Partition of Poland.