easiest way would be to leverage "democracy". there's less than 60k people living in greenland, probably about 40k of voting age and subtracting out us military personnel. offer them all $100,000 each and us citizenship if they vote for greenland to become part of the united states. how can denmark go against the voice of the people? go against democracy? if the people of greenland want to be part of the us, it would be authoritarian to not allow them that freedom. right of self-determination and all of that.  > approximately 88 percent of greenlands population is greenlandic inuit, an indigenous group of people. these people rely on traditional methods of obtaining food, which mainly include fishing, hunting and gathering.  doubt they're all that local to the kingdom of denmark if they can get a better deal with the us.
United States