I've been tangling with these questions, and as they were brought up in the Romans in the New World thread I thought that they should get their own thread since there's some interest.
Basically, there's different competing theories about why Norse Greenland ended. These are:
1. Inuit violence: The Inuit attacked the Norse and either wiped them out or made life so miserable for them that they left.
2. Starvation: the Norse's lifestyle was badly adapted to Greenland, and when the Little Ice Age started they could no longer provide food for themselves and all of them starved to death.
3. Emigration. Basically, Norway and Iceland were much more attractive places to live than Greenland for the Norse, and after land opened up due to the black plague, the Greenlanders just pulled up stakes and moved there. The fact that the crusades destroyed Greenland's economy by making elephant ivory more available to Europe's markets did not help, as now the Greenland Norse could no longer sell walrus ivory competitively.
So, where do people think the evidence points, and why? What's your pet theory?
Personally, I don't think that Inuit violence can be discounted. Reports to the Bishop if Iceland spoke of Inuit attacking and murdering more than a dozen Norse in one raid, and kidnapping a woman and two boys. For a small society such as the Norse colony, such a loss would have been very grave.
There doesn't seem to be mass graves of Norse slaughtered with stone weapons, so I don't think the Inuit are actually responsible for genocide against the Norse, but their harassment of the colony must have made life very unpleasant for the settlers. There probably was a mixture of conflict and peace between the communities, but ultimately they were two different peoples in competition for scarce resources, so friction must have existed.
(Alas, I don't have my Smithsonian book on the Norse in the North Atlantic on hand for the discussion, but hopefully I can pick it up later and actually have some facts to back up my assertions

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