See US's Treaty of the Danish West Indies:
> During 1916, the two sides agreed to a sale price of $25,000,000, and the United States accepted a Danish demand for a declaration stating that they would "not object to the Danish Government extending their political and economic interests to the whole of Greenland".
https://en.wikipedia.org/wiki/Treaty_of_the_Danish_West_Indi...
I'm reminded of the Budapest Memorandum (Russia's promise not to invade the Ukraine if the Ukraine gave up its nuclear weapons): https://en.wikipedia.org/wiki/Budapest_Memorandum.