AHC: Greenland in the US

Because we all love the idea of a vastly larger United States, how do we get Denmark to accept the US offer to buy Greenland?

Bonus points, just for funzies and that rare Greenland wank, how do we then get the US to then somehow become part of Greenland rather than the other way round?
 
After an able archer style nuclear war in the 80s, large parts of the civilized world is destroyed, but some bastions of civilization remain, one of the few in the Northern Hemisphere being that of the Jarldom of Greenland. In Nuuk, now a fortress city, and retaining some knowledge, like how to smelt steel, some 1600s technology, and some gunpowder manufacturing, the Overlords of the City, which also controls Iceland, and scattered inhabited artic territorys, plot Raiding misssions against the coast of America, which is claimed in the name of Odin.

They remember that their ancestors worshipped he upon the cross, but in the deluge of flame, and the arrival of the Fimbrul Winter, they returned to the worship of the Old Gods, and now claim a new land for the Glory of Odin.

The Second Age of the Vikings has arrived
 
Top