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, a stance he robustly reaffirmed on his first day in office, earlier this week. While American expansion hasn’t been discussed much in recent times, the proposal to buy Greenland makes more sense if one understands the history of the Arctic.