"He's not even talking to Greenland - he's talking to Denmark about buying Greenland."Read more
President Trump was upset at Denmark rejecting his idea of buying Greenland. But Denmark has sold territory to the United States before. The BBC's James Robbins reports. (Picture: General view of the the town of Kulusuk, in Greenland. Credit: AFP/Getty)
Denmark said the president's bid to buy Greenland was "absurd" - he called that offensive to the US.
Danish Prime Minister Mette Frederiksen has said she is annoyed and surprised at President Trump's decision to postpone a visit amid a spat over the future of Greenland.
US President Donald Trump is said to have discussed the idea of purchasing Greenland, an autonomous Danish territory, during dinners and meetings with advisers.
Apparently, such a transaction is unlikely to happen today, but back in 1800s and early 1900s, countries could acquire territory through business deals.
However, law professor Joseph Blocher wrote in 2012 that the "market for sovereign territory seems to have dried up".
"To be sure, there is still an active market for proprietary interests in public land... But borders - sovereign territory, rather than property - do not seem to be for sale."
"Sovereign territory was bought and sold throughout much of American history... But no such market currently exists," he wrote in his paper Selling State Borders.
As for Greenland itself, the territory has said that purchasing it would be out of the question.