The Duchy of Holstein was established by a Scandinavian monarch under what union?
Duchy of Holstein The Duchy of Holstein (German: "Herzogtum Holstein" , Danish: "Hertugdømmet Holsten" ) was the northernmost state of the Holy Roman Empire, located in the present German state of Schleswig-Holstein. It was established when King Christian I of Denmark had his County of Holstein-Rendsburg elevated to a duchy by Emperor Frederick III in 1474. Holstein was ruled jointly with the Duchy of Schleswig by members of the Danish House of Oldenburg for its entire existence.
Augusta of Denmark Princess Augusta of Denmark (8 April 1580 – 5 February 1639) was the third daughter of King Frederick II of Denmark and Sophia of Mecklenburg-Güstrow, and Duchess of Holstein-Gottorp as the wife of Duke John Adolf. She was politically influential during the reign of her son, Duke Frederick III.