New Delhi, Sept. 21 -- A new Greenland security deal gives President Donald Trump a triple win: smoother relations with the European Union, stronger Arctic security, and potential access to massive mineral reserves. Actually extracting those resources won't be simple, though.

Trump announced on Friday he had reached an agreement with Denmark and Greenland that gave the U.S. "permanent control" over Greenland's security, while backing down from threats of annexing the semiautonomous Danish territory.

Greenland has been an interest of Trump's since his first term as president, when he first floated the idea of buying the territory from Denmark. Melting ice caps in the Arctic has made the territory the new security frontier in tensions bet...