The 21st-century American president who by all accounts is most appreciated by the people of Denmark and the rest of the world, Barack Obama, is scheduled to travel to the Danish city of Aalborg in late September. So, presumably, the Danes were not overly broken up over the decision Wednesday by President Trump to cancel a planned visit earlier in the month.

But the president’s latest tantrum should concern Americans for two reasons.

First, Trump needs to get out more. It is important for him to visit countries where, if he pays even the slightest attention, he will recognize that his policies and pronouncements are not going over well. The people of Ireland and the people of Britain delivered the message, with very creative and very large protests in June, as the Danes surely would have in September. This president needs the feedback—even if he fears it; as he surely feared comparison of his reception in Denmark with that of Obama.

Second, and more importantly, Trump’s stated reason for abruptly canceling the planned state visit—as absurd as it was—has about it echoes of an especially foul imperialism. Trump tweeted the news of his decision with an announcement that “Denmark is a very special country with incredible people, but based on Prime Minister Mette Frederiksen’s comments, that she would have no interest in discussing the purchase of Greenland, I will be postponing our meeting scheduled in two weeks for another time.”

What offended the president was the reaction of the prime minister to reports that Trump is interested in buying Greenland—an autonomous country of the Kingdom of Denmark—from the Danish government. Frederiksen dismissed the prospect as “an absurd discussion.”

“I strongly hope that this is not meant seriously,” she said. “Greenland is not for sale. Greenland is not Danish. Greenland belongs to Greenland.” The prime minister’s statement was diplomatic; indeed, she emphasized a desire to maintain close relations with the United States. “Developments in the Arctic call for further cooperation with the US, Denmark, Greenland and the Faroe Islands,” she said, ”and I’d like to underline that still stands.”

Trump’s response was a tirade. The prime minister, he claimed, was being “nasty.”

“I thought it was not a nice statement, the way she blew me off,” he told White House reporters on Wednesday morning. “She shouldn’t treat the United States that way,” the president grumbled. “She said ‘absurd.’ That’s not the right word to use.”

But “absurd” most definitely is the right word to use. Or, at least, one of the right words. As Søren Espersen, the foreign affairs spokesman for the Danish People’s Party, said, “If he is truly contemplating this, then this is final proof, that he has gone mad. The thought of Denmark selling 50,000 citizens to the United States is completely ridiculous.”

Trump likes to recall that there have been instances when governments—including that of the United States—have sold islands, and regions of continents, to other governments. But the notion that peoples and the places where they live can in the modern age be bartered off in what the president refers to as “a large real estate deal”—and what some in his administration appear to see as a chess move in a global game with China—is, as Greenland Premier Kim Kielsen says, “not something to joke about.”

Trump’s talk should offend everyone who respects the right of self-determination.

The Universal Declaration of Human Rights, a 71-year-old document, begins with “recognition of the inherent dignity and of the equal and inalienable rights of all members of the human family” and explains that respect for this basic premise is “essential to promote the development of friendly relations between nations.” It also declares that “no distinction shall be made on the basis of the political, jurisdictional or international status of the country or territory to which a person belongs, whether it be independent, trust, non-self-governing or under any other limitation of sovereignty.”

In other words, President Trump has absolutely no right to buy Greenland, or to meddle with Greenland’s future. The 56,000 people of Greenland, a vast country with immense natural resources, are supposed to chart their own course. It is true that Greenland is currently aligned with Denmark. But, as Frederiksen has repeatedly, and correctly, explained, “Greenland is not Danish. Greenland is Greenlandic.”

Greenland has since the 1970s moved toward greater self determination, adopting home rule after a 1979 referendum vote and since 2009 (under its Self-Government Act) has managed the vast majority of its own affairs. While the Danish government still has charge of defense and foreign relations, Greenland has its own parliament, and there is a large Greenlandic independence movement.

The current premier, Kielsen, leads Siumut, a social democratic party that has a history of advocating for independence for Greenland. Polling shows widespread support for independence, although there are plenty of debates about how quickly the process might proceed. “When you follow the discussions on Arctic matters among Danish politicians,” says Ebbe Volquardsen, the head of the Department of Cultural and Social History at the University of Greenland, “it has become clear that a future Greenlandic independence now at least is seen as a possibility, which has changed the ways in which Danish-Greenlandic relations are addressed.”

For those of us who believe that countries with small populations and big ideas are essential to the global discourse—because they are often more courageous and innovative in advancing policy solutions and embracing international initiatives on issues such as the climate crisis—the prospect of Greenlandic independence is compelling. But decisions about Greenland’s sovereignty cannot be made by those of us who do not reside in Greenland. And those decisions should never be meddled with by an American president. The people of Greenland must make their own choices about their own future. And Trump must recognize that Prime Minister Frederiksen speaks a universal truth when she says, “Thankfully, the time where you buy and sell other countries and populations is over.”