Kalmar Union, combination of the three crowns of Denmark, Sweden, and Norway, effected at Kalmar, Sweden, by Queen Margaret I Margaret I, 1353–1412, queen of Denmark, Norway, and Sweden, daughter of Waldemar IV of Denmark. She was married (1363) to King Haakon VI of Norway, son of Magnus VII of Norway and Sweden.
..... Click the link for more information. in 1397. Because the kingship was elective in all three countries, the union could not be maintained by inheritance. Nationalist forces used the election procedure to modify terms of the union. Margaret's successors controlled Sweden only for brief periods; the accession (1523) of Gustavus I Gustavus I (gəstā`vəs)
..... Click the link for more information. as king of Sweden dissolved the union. The union of Denmark and Norway lasted, however, until 1814.

Kalmar Union

(1397–1523) Scandinavian union that joined the kingdoms of Norway, Sweden, and Denmark under the rule of a single monarch. Margaret I had become regent of the three kingdoms by 1388; she chose her grandnephew Erik of Pomerania to become their king, and he was crowned at Kalmar, Swed., in 1397. Each country kept its own laws, customs, and administration. Sweden rebelled and claimed independence under Gustav I Vasa in 1523, and Norway became a Danish province in 1536.