How the US could take over Greenland and the potential challenges

U.S. President Donald Trump has repeatedly threatened Greenland and says Washington must take control of the strategically located island. The White House says military options are being considered. But Denmark's prime minister warns that would spell the end of NATO. Greenlanders oppose becoming part of the U.S. The United States already has a military base there under a 1951 defense agreement. Trump says control is needed for security against Russian and Chinese threats. But Greenlanders say they want independence and not U.S. annexation.