system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What would happen if the Crown Prince of Denmark were to marry the Crown Princess of Sweden and they had a child?

What would happen to the respective countries and their monarchy? Would they merge to become one nation? Obviously discounting current children, I am curious.
gpt
The child would be the monarch of two different countries, in a situation called a personal union.  The countries would remain separate.

And since the succession runs through different bloodlines, and different countries, have different rules of succession, they could easily wind up with different rulers.  If that monarch had no children or siblings, one of his father's relatives would wind up on the Danish throne, and one of mother's on the Swedish throne.