Trump already has open door to grow U.S. military presence in Greenland thanks to a little-known Cold War-era agreement between the U.S. and Denmark

President Donald Trump’s yearslong threats to take over Greenland have crescendoed this week. On Wednesday, White House press secretary Karoline Leavitt said Trump is considering a range of options in pursuit of the country, and that “utilising the U.S. military is always an option at the commander-in-chief’s disposal.”

But according to foreign policy experts, Danish officials have been baffled by Trump’s threats to resort to military intervention to gain control of Greenland because there’s already a long-standing agreement in place for the U.S. to increase its military presence there. In 1951, the U.S. and Denmark signed a little-known defense agreement allowing the U.S. “to improve and generally to fit the area for military use” in Greenland and “construct, install, maintain, and operate facilities and equipment” there. 

“This agreement is very generous, it’s very open,” Mikkel Runge Olesen, a senior researcher at the Danish Institute for International Studies in Copenhagen, told Fortune. “The U.S. would be able to achieve almost any security goal that you can imagine under that agreement.”

Given the wide-reaching terms of the contract, “there is very little understanding as to why the U.S. would need to take over Greenland at this time,” Olesen added.

Though Trump’s desire for Greenland has punctuated both of his administrations (in 2019, his intentions to buy the self-governing Danish territory were immediately rebuffed by Danish Prime Minister Mette Frederiksen), world leaders have taken the president’s most recent interest in the island more seriously. Following the U.S. forces’ capture of Venezuelan leader Nicolás Maduro, Trump has invoked greater imperial authority through what he has endorsed as the “Donroe Doctrine,” alluding to the 19th century Monroe Doctrine, a foreign policy warning European powers against intervention in the western hemisphere. 

Greenland—covered in ice and home to 56,000, mostly Inuit people—has become crucial to the defense of North America thanks to its positioning above the Arctic Circle giving it access to naval and shipping routes. Combined with its abundance of rare earths, the country has become coveted by Trump, who wants to secure it not only for its wealth of natural resources, but also against the Chinese and Russian ships he claims have anchored themselves in the Arctic region.

Long-standing U.S.-Danish ties

For more than 80 years, the U.S. has had a presence on Greenland, which became a foundational part of its deepening relationship with Denmark—and the North Atlantic Treaty Organization (NATO). During WWII, Danish ambassador to the U.S. Henrik Kauffmann, defied the Nazi-controlled Danish government and essentially brokered a deal with the U.S. to give America access to Greenland. A U.S. military holding there would prevent Nazi forces from using the island as a bridge between Europe and North America.

The deal that was supposed to dissolve after the war was instead bolstered by the creation of NATO in 1949, which obligated the U.S. to provide defense for Europe against Soviet forces. A new agreement in 1951 confirmed the U.S.’ rights to establish defense areas in Greenland, and is contingent upon the continued existence of NATO to be valid. In 2004, the agreement was updated to add Greenland, which established some self-governance in 1979, as a signatory.

The U.S. has only one military base on Greenland today, the Pituffik Space Base, down from about 50 during the height of the Cold War. But should the U.S. want to expand its presence there for national security reasons, as Trump has suggested, it would require negotiations with Denmark and Greenland, Olesen said. Historically, those negotiations have been friendly.

“In practical terms, there has been a tendency on the Danish and the Greenlandic side to always look at us security requests in Greenland with a lot of goodwill and a lot of openness,” he said.

Danish Prime Minister Frederiksen, citing the 1951 agreement, implored the Trump administration to stop his talk of taking over Greenland.

“We already have a defense agreement between the Kingdom and the United States today, which gives the United States wide access to Greenland,” Frederiksen said in a statement over the weekend. “I would therefore strongly urge the United States to stop the threats against a historically close ally and against another country and another people who have said very clearly that they are not for sale.”

Trump’s motivations for taking Greenland

Garret Martin, lecturer and codirector of the Transatlantic Policy Center at American University, speculates Trump’s insistence on appearing to brush off the 1951 agreement in favor of military force or offers to purchase Greenland (despite Danish officials repeatedly saying the country is not for sale), is an extension of the 19th century “gunboat diplomacy” philosophy the president took with Venezuela.

In the case of Greenland, Trump could be wanting to send a message to Denmark the U.S. has greater military capabilities that it is willing to deploy.

“Trump believes—and is often very keen to emphasize—the United States as leverage,” Martin told Fortune. “And it’s possible he’s trying to tell Denmark, ‘Look, you are in a position of weakness. Greenland really fundamentally depends on us. Why should we have to avail ourselves of those formalities when really we’re the key player?’” 

Trump’s tactics could also come from a desire to stake claim over the rare earth metals buried deep under the Greenlandic ice, which has become more urgent to Trump as China sits on 90% of the rare earth the world needs.

Anthony Marchese, chairman of Texas Mineral Resources Corporation, told Fortune earlier this week the president’s hope of mining those rare earths is nearly a fantasy. The northern part of Greenland is mineable only six months out of the year due to treacherous weather conditions, and expensive mining equipment has to endure months in that cold climate.

“If you’re going to go to Greenland for its minerals, you’re talking billions upon billions upon billions of dollars and extremely long time before anything ever comes of it,” he said.

According to Olesen, Trump’s desire for rare earths, as well as his national security urgency, can be addressed by Danish and Greenlandic officials through negotiations, making them less of a concern. The trouble will be if Trump’s biggest motivator to move into Greenland is a symbolic show of military prowess rather than specific demands that can be addressed through diplomacy.

“It’s hard to compromise with territorial expansion,” Olesen said.

This story was originally featured on Fortune.com