I'm having a debate with a Danish man who is convinced that the Kalmar Union was a single kingdom whereas I argue it was a personal union between three individual kingdoms under one king who had their own power to govern what they wanted to do in the union.
There is always more to say, especially in such a complex area as this, but while you are waiting for fresh responses to your query, you might like to review this earlier answer of mine, which goes into some detail about the ways in which the outcomes of the Union of Kalmar, especially the manner in which Danish sovereignty was actually imposed in Sweden, bore on the Stockholm Bloodbath of 1523. The answer discusses the difficulty that Danish kings had in imposing what was indeed a personal union on a local nobility that actively resisted "foreign" intervention.