What has changed is that this treaty directly with Greenland and Denmark, outside of NATO, becomes the Law of the Land in the US, 'forever', independent of NATO. Under the American Constitution, any treaty signed by the US is so entrenched that no Act of any legislature, nor even of the President himself, can legally order military action in contravention of that treaty. And under the Military Code and under general law, no military officer can obey an order that is not legal. Basically, it completely prevents Trump from issuing a legal order to invade Greenland. I am sure his military leaders will tell him this. In essence it completely protects Greenland from ever being taken over by America, with almost no gain by America except for access to the mineral resources. Incidentally, I see nothing that would prevent DENMARK from entering into an agreement with any another country to develop Greenland's resources through a Danish company.