Sort of. The modern concept of a nation is pretty recent, so you have to think in terms of hereditary kingdoms. The interesting thing is that it was possible for a monarch to inherit not just one kingdom, but two or three. The kingdoms would sometimes merge in the legal sense (a "real union"; think the modern UK), but not necessarily. Sometimes you just had the same guy wearing two different (very ornate) hats as the king of two legally distinct kingdoms. This is called a "personal union", since the kingdoms were united not by laws, but were united "in the person" of the monarch.

That was the case from 1397 to 1524, during which the King of Denmark was also the King of Norway and ALSO the King of Sweden. After Sweden broke off in 1524, the Kingdoms of Denmark and Norway were united in a "real union" with Norway as the junior partner. This lasted until 1815 when Norway made an unsuccessful bid for independence and Denmark was forced to cede Norway to Sweden due to politics surrounding the Napoleonic Wars (during which time the idea of a modern nation state was starting to become more of a thing).

This is all a massive oversimplification (it's super messy) and I'm certain I'm making some real historians eyes twitch, but that's the best TLDR I can give you.