US and Europe
The Kingdom of Denmark is a member of NATO since its inception, and Greenland is covered by the security guarantees of NATO. The US Has had a military presence in Greenland since the 1950s, and it has a base there. It has consequently, over the years, drawn down its presence there. So if there's any security gap, the US bears partial responsibility for it. And if it wants to fill that security gap, it has all the treaties and mechanisms it needs either bilaterally with the Kingdom of Denmark or through NATO to ramp up its security presence there."
