His message to Denmark makes it clear that this is a toddler’s temper tantrum, and that giving in will only make things worse:

Dear Ambassador:

President Trump has asked that the following message, shared with Prime Minister Jonas Gahr Støre, be forwarded to your [named head of government/state]

“Dear Jonas: Considering your Country decided not to give me the Nobel Peace Prize for having stopped 8 Wars PLUS, I no longer feel an obligation to think purely of Peace, although it will always be predominant, but can now think about what is good and proper for the United States of America. Denmark cannot protect that land from Russia or China, and why do they have a “right of ownership” anyway? There are no written documents, it’s only that a boat landed there hundreds of years ago, but we had boats landing there, also. I have done more for NATO than any other person since its founding, and now, NATO should do something for the United States. The World is not secure unless we have Complete and Total Control of Greenland. Thank you! President DJT”