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.
Eric I, Duke of Schleswig Eric I Abelsøn (died 27 May 1272) was a Danish nobleman. He was the ruling Duke of Schleswig from 1260 until his death in 1272. He was the second son of King Abel of Denmark, Duke of Schleswig and Mechtild of Holstein.