Your reliance on the 1916 treaty ignores how that deal was actually reached. The treaty was finalized only after US Secretary Lansing issued a "plain spoken threat"[1] to seize the islands if Denmark refused to sell. Thus the agreement is not proof sovereignty is inviolable, but rather a precedent that the United States is willing to use coercion when it perceives an existential threat. Same as the US feared Germany then, fears of Russia and China today could lead the current administration to again pull a page out of Lansing’s book and use similar pressure to secure Greenland

[1]https://www.execfunctions.org/p/the-danish-west-indies-prece...

Do you believe it’s justified? What’s the point of treaties if the agreement isn’t inviolable?

Reserving judgment on the particular case at hand, rebus sic stantibus as well as self-preservation/national security are accepted avenues for modifying treaties (or adherence thereto) with a fair amount of precedent.

Isn’t that basically grounds for no country to respect the international order or laws or stability? Why would anyone care when the biggest powers can choose to abandon it at will. Laws for everyone but not for America (or Russia or China)?

Why do you think NATO exists, or has a need to exist?

You misquote. The article says that the islands may be seized if they were transferred to another European power, and especially if transferred to Germany. The article does not that they would have simply been seized regardless.

Go to the primary source. https://history.state.gov/historicaldocuments/frus1914-20v02...

It's clear that the threat of Denmark falling into the hands/influence of another power, not the fall itself, was enough. In case it wasn't clear, Lansing writes "the possible consequence of absorption," not, "the absorption of Denmark."

The US position was that Denmark was too small and weak to remain neutral or defend the islands. Therefore, as long as the islands remained Danish, they were a security risk to the US.