The Kalmar Union was a solidification of the throne which united three kingdoms, Denmark, Norway with Iceland and Greenland, and Sweden with Finland under one common ruler. Each time a new monarch took the throne a new constitution was formed which regulated the power between the high nobility represented by the Council and the joint Scandinavian royal powers.
The Swedish nobility’s dissatisfaction with the Danish domination led to Sweden taking themselves out of the union, while Norway continued in union with Denmark. After King Christan II’s attempt to eradicate Sweden’s nobility in the bloodbath of Stockholm in 1520, Gustav Vasa was chosen as King of Sweden. This caused the dissolution of the Kalmar Union. The Oldenburg and Vasa dynasties still insisted on their claim to the northern thrones, which became grounds for wars between these countries in the centuries which followed.
From the Norwegian Wikipedia, the free encyclopedia at: http://no.wikipedia.org/wiki/Kalmarunionen