I find it somewhat interesting that the whole "immovable borders" idea started around the end of World War II. Like, that's it. The borders can't move anymore. Well, expect for Israel and USA. Israel gets infinite tries, and USA got the chance in the Iraq war, but that was super duper it. It's an interesting thing to ponder. It's not a natural state of events, obviously, from a historical perspective.
It's even weirder when you consider the thing they say about Greenland, i.e. that they have a right to self determination. Wouldn't that mean you can vote your way into annexation? Well, Crimea shows you can't. I get the validity is disputed, but the people who voted
felt like they were represented and at any rate, nobody seems to consider it as an option. Musk one
suggested UN should hold referendums watched over by UN to check the validity of Donbas annexation, but that wasn't seen as acceptable even with fraud removed.
So, Greenland has a right to self-determine, but no right to choose USA. That's a weird conundrum. USA, for example, is very clear on the matter of its states - they have no right to self-determine their association to the Union. Other countries say the opposite.
To the extent we believe democracy to be an instrument by which the will of the people is expressed, wouldn't the best option be to give US a chance at a referendum? If it works, Greenland is happy. If it doesn't, US claims are rejected on world stage. It's the final peaceful solution before violence even need be considered.