Indeed this concept of hemispheres to justify military action is total nonsense, the Prime Meridian could have been placed anywhere. Strictly speaking, the whole of Ireland may be invaded by the USA according to this "doctrine".
I didn't mean to imply that. I was only speaking of how pragmatic it would be for European powers to handle the logistics to fight a land war in Greenland. The US can project power basically anywhere, but it's harder for smaller navies to pull that off.
As far as the logistics go: in 1982 the UK managed to land several regiments on the Mal^W Falkland Islands (13'000 km); surely it'd be easier to do similar, over much shorter distances?
Note: if AR (a client state* of the US at the time) had been hoping the Monroe Doctrine would be put into practice for them, that hope was in vain.
https://news.ycombinator.com/item?id=41564406
(who'd want to invade IE anyway? They have no culture beyond a pair of shite gaelic rappers and they're so backward they still travel on horseback: https://www.youtube.com/watch?v=ljPFZrRD3J8 )