The young men will not tight to defend their country from Russia, but they are going to line up for Greenland?
It doesn’t make sense
“they are going to line up for Greenland?”
Greenland has been politically and culturally associated with Denmark (and previously the Dano-Norwegian Realm) for roughly 1000 years since the Viking age and the vast majority of Greenlanders have some Danish or European ancestry.
So Danes may feel a close cultural tie with Greenland.
That being said - militarily Denmark stands zero chance against the USA, especially considering that the USA already has a large number of troops already on the island.