A random Norwegian guy had a hot temper, and that's why Greenland is part of the Kingdom of Denmark today.
Erik, called 'the Red' for his temper, killed a guy, got outlawed, and went to Iceland.
Killed a guy, got outlawed, and went to Greenland and he convinced a bunch of people to go there. A settlement was established.
Later Norway claims Greenland (and Iceland and Faroe Islands).
In the Medieval period Denmark enters in a personal union with Norway, including the islands. In practise Norway becomes part of Denmark.
The Little Ice Age comes and the contact to Greenland is patchy for a few hundred years. In 1721 it is re-established, and Denmark affirms its claim to Greenland.
In 1814 Denmark loses Norway to Sweden but keeps the North Atlantic Islands.
And thus, because of Norweigan Erik's terrible temper Greenland is Danish today.