Can Trump legally apply tariffs on US allies over Greenland?

The short answer, under international law, is no: The use of coercion to acquire another country’s territory is forbidden. The question arises since President Donald Trump threatened on Saturday to impose new tariffs on several European countries unless Denmark sells Greenland to the United States. He said that the United States must purchase Greenland to safeguard its national security and ensure “world peace.” As a matter of domestic law, however, the US president has no authority to apply tariffs for this purpose.
The president does not have the authority to acquire territory on his own.…