President-elect Trump’s talk of territorial expansion has rattled world leaders at an already precarious time in global politics. Trump doubled down last week on his suggestions that the U.S. buy Greenland, take control of the Panama Canal and make Canada “the 51st state.” He declined to rule out “military or economic” coercion against either Greenland or the canal, and he said he was open to using “economic force” on America’s neighbor to the north.