Purchasing Greenland is honoring their sovereignty. For example in 1917 we bought the virgin islands from Denmark with a population of around 30,000 for $25 million in gold coin. So we could, in theory, purchase Greenland from Denmark with a population of around 55,000 for an amount in gold coin.

Of course like everything Trump says, he has a big consequence if little conditions are not met. So while everyone is looking at the big consequence of buying Greenland from Denmark nobody is looking at the little conditions he wants. So Trump wants Denmark to pay more for defense for Greenland to be able to keep Russia out, which they announced 2 hours after he offered to purchase Greenland that they are spending $1.5 billion on additional military aid including inspection ships, long range drones, dog sled patrols and airport upgrades (where no doubt our aircraft can land). Another little condition he wants is for China to get out of Greenland and to get the west/US in. For example Chinese companies have been investing in Greenland’s rare earth sector, Shenghe Resource, a shanghai listed company has a stake in the Kvanefjeld project and Kringlerne project in Greenland. All existing rare earth mines outside China, except for those in Russia and one mine in Australia, Mount Weld, export their minerals or concentrates to China. We would want these rare earth minerals in Greenland mined by the west so it goes to our industry instead of China's.

Also Greenlanders are not subsistence hunter/gatherers, many go to school in Denmark and their small mixed economy is based on fishing, construction, tourism and of course the massive government subsidies.

So whether we buy Greenland or not, I expect to see more military spending in Greenland and I expect to see less China development and more western development. Russia out, China out and the US in whether we buy it or not.