India, Jan. 21 -- US President Donald Trump spoke at Davos and Greenland kept coming up. He ruled out military invasion to take the Arctic territory, but he reaffirmed his conviction that Greenland is of vital importance to US security. His comments calmed nervous financial markets and the stock market reversed earlier losses-but they also raised new questions about diplomacy, self-determination and the growing scope of America's strategic ambitions in the Arctic. Greenland has a population of less than 60,000 people, but it's at the center of an emerging geopolitical rivalry as melting ice opens new shipping routes and changes military equations.

Speaking to a mix of business figures and politicians, Trump made it clear that force was n...