https://theconversation.com/greenland-is-rich-in-natural-res...
Greenland is either about Trump intentionally causing chaos with NATO for the benefit of Russia (depending on your politics), or it's the Pentagon & Co. looking to lock down strategic territory for the near future superpower stand-off with China, which will be a global conflict (and may involve China and Russia on one side). Controlling Greenland and Alaska would provide the US with enormous Arctic Ocean positioning. Now what does that have to do with China you may ask? Trade, transit and military asset positioning. The US is looking to secure what it regards as its hemisphere, while China is about to massively push outward globally with a projection navy. The US has less than ~20 years to lock down its hemisphere (again, what the US believes to be its hemisphere) before China starts showing up with its navy everywhere. There will be constant navy-navy challenges everywhere. China will constantly probe the US points of control, for all the obvious reasons. The US will want to keep China as far away as possible.
The US only recognizes two threatening competitor powers in the world today: China and Russia. Russia is of course not what it was during the Soviet era. However a long-term partnership with China would change the dynamic a lot. Russian territory may come to host major Chinese ports in time. For the right price it's extremely likely that China can buy a multi port deal in the Arctic Ocean region from Russia. It'd be invaluable access & projection potential for China. Any superpower would want that realistically.
The US has militarily defended Greenland since 1941. As of 2020 Denmark's Arctic Command has one aircraft, four helicopters, four ships, and six dog sleds to patrol the entire island, three times the size of Texas.
Greenland claims to welcome outside investment. In practice, however, Nuuk never approves anything related to resource development. More on this below.
Denmark no longer "owns" Greenland in the way the US owns Alaska, or even Puerto Rico; Greenland can declare independence on its own at any time, unlike the latter. What the Danish parliament allowed in 2009 it can in theory undo, but Greenland can also declare independence at any time.
While Greenland has stated its willingness to continue to host US troops after independence, there is always an uncertainty from having to depend on a foreign government.
Annexation would also simplify US access to Greenland's natural resources, which (the SACEURs above also mention) are as vital to the US as its location is. For all of Greenland's claims that it seeks outside investment, in practice it leeches €600 million from Copenhagen annually (only for domestic use; Denmark handles all foreign/military affairs) for its 50,000 people and turns down almost every attempt to develop mines and oilfields, allegedly because of environmental concerns. And why should it allow such attempts, when it has the best of all worlds now, with Denmark and the US paying for everything?
Greenland a) is inevitably going to gain independence—every single poll for decades has shown this—but b) is completely unable to function on its own as a bona fide independent country. Pacific islands (barely) function as independent countries because their tiny populations are commensurate with their small areas. Greenland's 50,000 people live on an island that is, as noted, three times the size of Texas. Denmark is completely unable to defend Greenland militarily (thus the US presence there in the first place); Greenland certainly cannot, given that it can't function today without the aforementioned €600 million for just domestic affairs. Given this, US annexation or affiliation is inevitable.
"The US invading Greenland would destroy NATO!", you say. I don't believe that the US would invade Greenland militarily; it will likely buy it, affiliate with it through a Compact of Free Association à la Palau, or obtain some sort of ironclad investment rights not dependent on whether Greenland is part of the Kingdom of Denmark or independent. But let's say that the US does, and NATO dissolves.
It comes down to net benefits. Would owning Greenland be more valuable for American national security, than the current NATO status quo of the US being willing to to accept its own cities being nuked if Russia invades Western Europe?
The calculus made more sense (if it ever did) during the Cold War, when NATO ended at Germany's eastern border. Does it make sense now, when Montenegro is a NATO member? I strongly suspect that the answer is not one that the rest of NATO would want to hear, regardless of the Ukraine War.
I think the US may just remain secure without owning Greenland. I mean it's done ok so far.
China is going to end up being every bit as powerful as the US ever was, both economically and militarily. Nothing will be off the table in what's coming. Russia has never had a true global projection navy, China will have a navy that is plausibly going to be both larger and more powerful than the US navy with full global reach. That global reach will include the entire North and South American region.
If you're the US you look to lock down Greenland and Panama, for starters.
We now live in a world that knows for a fact a deal with the US is worth nothing and can not even be relied upon to last more than six months.
Countries and allies that made trade deals with Trump after he destroyed existing deals are now seeing further petty tariffs being applied by what appears to be a giant baby.
All the movements of plastic ships and little horses on a Risk map aside, the steady undercurrent of reliable trade and markets is headed out the window in an act of self defenestration.