Duchy of Holstein

The Duchy of Holstein was the northernmost state of the Holy Roman Empire, located in present-day Schleswig-Holstein. It was founded in 1474 when King Christian I of Denmark's County of Holstein-Rendsburg was elevated to a duchy by Emperor Frederick III. Members of the Danish House of Oldenburg ruled Holstein, often jointly with the Duchy of Schleswig, throughout its existence. From 1490 to 1523 and again from 1544 to 1773, the Duchy was partitioned between various Oldenburg branches, including the dukes of Holstein-Glückstadt and Holstein-Gottorp. The Duchy of Holstein ceased to exist on October 30, 1867, after the Kingdom of Prussia annexed it in 1866 following the Austro-Prussian War.