The US has long since wanted to purchase Greenland, not "fight" them, for strategic reasons. I'm not sure why there is this fantasy that the US is going to fight the Greenland people? Honestly.
“But we need it really for international, for world security, and I think we’re going to get it. One way or the other, we’re going to get it,”
-- Donald Trump, March 4, 2025
Because the US was threatening to take over Greenland by force maybe? There's a reason Denmark rushed soldiers there.
The president of the United States literally said that they were going to get Greenland, one way or another.
If I were to say "I'm going to get Dionian's house, one way or another" would you not prepare yourself for an invasion?