I think the advent of the Little Ice Age is what doomed the outlying settlements. The first settlements began during the Medieval Warm Period, but when the Ice Age set in they were frozen out and cut off (the local aborigines and the plague behind them in Europe didn't help either.)
"I think the advent of the Little Ice Age is what doomed the outlying settlements."
There was an archaleologic show (Discovery channel??) about this that I found interesting. When the Viking settlements died off in Greenland the cold weather made farming harder/impossible to support enough people. The locals (inuit-type???) adapted and did their whale/seal/hunting stuff. The Vikings by then had become Christian. I'm thinking the archaelogist had some type of evidence (or it may have been speculation) that the Vikings didn't go for the "heathen" rituals involved before and after the hunts, and therefore died off and/or abandoned the settlements.