Donald Trump spent a noteworthy chunk of the transition period provoking controversy—and insulting NATO allies—with his proposals for expanding the U.S. Maybe most prominently, he has repeatedly discussed buying Greenland from Denmark,

From the Reconstruction era to the Cold War, multiple administrations have tried (and failed) to acquire the Arctic island. Here’s why Greenland has always remained out of reach—and why it always mattered so much.

Donald Trump’s renewed push for control of Greenland comes as Denmark announces a $2 billion Arctic defense upgrade. This upgrade points to the strategic value of an island that hosts America’s northernmost military installation and holds vast mineral wealth.