Along the retreating ice of the Arctic, where empires have long measured their ambitions, President Trump signed a security agreement with Greenland on Tuesday, committing the United States to new military installations in one of the world's most contested regions. The deal arrives as Russia and China deepen their own Arctic footprints, and as an American administration seeks to demonstrate resolve both to rivals abroad and to voters at home ahead of November's midterm elections. It is a moment that reveals how geography, once thought frozen and remote, has become a living theater of great pow