The US President publicly stated that Denmark does not have a clear „right of ownership” over Greenland.
„Why do they have a ‘right of ownership’? There are no written documents, just the fact that a ship arrived there hundreds of years ago, but we also had ships that reached there,” declared Donald Trump, reiterating a position expressed earlier on January 9.
But, surprise, there is a written document! And not just any document, but one signed by the United States.
In 1916, during the negotiations in which the US purchased the Danish West Indies, the then American Secretary of State, Robert Lansing, signed an official declaration explicitly recognizing Denmark's right over Greenland. The text is difficult to creatively interpret.
"The Government of the United States of America will not object to the political and economic interests of the Danish Government being extended over the entire Greenland," states the declaration signed by Lansing in New York on August 4, 1916, discovered by The Guardian.

In other words, the document that Trump claims he can't find exists, is written, signed, and originates from the American diplomatic archives. Furthermore, it unequivocally acknowledges Denmark's sovereignty over the entire Greenland.
The 1916 declaration is considered an important diplomatic milestone in establishing the international status of the Arctic territory. But since when does a piece of paper of this kind matter to the great orange leader? He's still upset that he didn't win the Nobel Prize, even though Maria Corina Machado went to the White House specifically to give him the medal.
