The Duchy of Holstein was established by a Scandinavian monarch under what union?
Christian I of Denmark Christian I (February 1426 – 21 May 1481) was a Scandinavian monarch under the Kalmar Union. He was King of Denmark (1448–1481), Norway (1450–1481) and Sweden (1457–1464). From 1460 to 1481, he was also Duke of Schleswig (within Denmark) and Count (after 1474, Duke) of Holstein (within the Holy Roman Empire). He was the first Danish monarch of the House of Oldenburg.
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.