Denmark's Prime Minister Mette Frederiksen is drawing a bright red line over Greenland, and she's using the biggest diplomatic weapon in her arsenal to do it: threatening NATO's survival.

In response to President Donald Trump's ongoing push to acquire the Arctic island, Frederiksen told Danish broadcaster TV2 on Monday that military action against Greenland would be one NATO ally attacking another. That kind of move, she said, would effectively blow up the entire alliance.

The End of NATO

"I believe one should take the American president seriously when he says that he wants Greenland," Frederiksen said, according to a translation cited by Bloomberg. "But I will also make it clear that if the U.S. chooses to attack another NATO country militarily, then everything stops, including NATO and thus the security that has been established since the end of the Second World War."

The logic is straightforward: Greenland is a semiautonomous territory within the Kingdom of Denmark, which means it's covered under NATO's collective security framework. An attack on Greenland would be an attack on Denmark, period.

Trump's Strategic Argument

Trump isn't backing down. Speaking to reporters Sunday, he described Greenland as "so strategic right now," pointing to what he characterized as significant Russian and Chinese naval activity around the island. "We need Greenland from the standpoint of national security, and Denmark is not going to be able to do it," Trump said.

The president has repeatedly emphasized the Arctic's growing geopolitical importance, with both Russia and China expanding their presence in the region. From his perspective, controlling Greenland is a matter of American security interests.

Frederiksen pushed back hard on those claims. She pointed out that Denmark already provides the United States with extensive military access to Greenland, and that Washington has zero legal basis to annex the territory. She also noted that Greenlanders themselves have made abundantly clear they're not for sale.

European Pushback Intensifies

Last week, Frederiksen and Greenland's Prime Minister Jens-Frederik Nielsen jointly rejected Trump's annexation calls, stressing that the Arctic territory remains part of the Danish Kingdom and falls under NATO's collective defense umbrella.

On Monday, UK Foreign Secretary Yvette Cooper weighed in, reaffirming that Greenland's future is for Denmark and the Greenlanders to decide. German Foreign Minister Johann Wadephul echoed that message, emphasizing that Greenland is Danish territory and, as part of a NATO member state, is protected under NATO defense commitments.

The unified European response suggests Trump's Greenland ambitions are running into a diplomatic brick wall, with America's closest allies making clear that some things aren't negotiable.