The got was they already had. The US has been able to do pretty much everything the wanted in Greenland since the 2nd world war.
Its a very good deal for Denmark too, especially on the long term with a more sane person than Trump in charge. The benefit are good for both parties and gives Denmark a role of exclusive ally to US in the region, something like South Korea in the East Asia, before Trump broke with them too.
But at a steep price.
The US are selling more gas and more weapons to Europe. They have pretty much a monopoly on AI and data centre hardware, too, and pretty much tech in general. So the US have got this favourable deal and Europe has become more dependent on them, too...