At https://popular-archaeology.com/article/lost-norse-of-greenland-ivory-tr… … courtesy of the University of Cambridge. The Viking colonies on Greenland were major settlements by the 12th century and Greenland even had its own bishop. However, later, by early 15th century, the Norse had vanished – leaving behind their ruined houses and farms. At first climate change was blamed as colder weather and sea ice around Iceland made it difficult to cope with sea voyages back and forth to Scandinavia. The old theory involved the farmers unable to adapt to these conditions. However, there is now good evidence to show the inhabitants had a diet high in fish and other marine creatures – so they would not have had to change their diet too much. Fingers have been pointed at the Black Death, which ravaged Europe in the late 14th century, but scepticism has persisted on the actual cause – with even a conflict with the Eskimo being vaunted. Now we have a new theory. For a couple of centuries the Vikings had a monopoly on the ivory trade into Europe. The Islamic world controlled the trade out of Africa and elephants were out of bounds. Walrus ivory on Greenland provided the necessary source of this easily carved material – during the 12th to 14th centuries. Walrus ivory has turned up in Trondheim, Bergen, Oslo, Dublin, London, and Schleswig etc – dated between 900 and 1400AD. Ivory from walrus came to dominate European cultures in the medieval period – but then disappeared (replaced by elephant ivory). One reason may be a trade breakthrough – the more convenient elephant ivory replacing walrus ivory. However, this change was also just after the Black Death epidemic – so it isn't necessary to think in terms of a collapse in walrus ivory as a commodity price issue. One might assume, like the authors, that unable to sell their walrus tusks the Vikings were trumped. If ivory sources from outside the Viking sphere became available the market could have collapsed (abd this is the thrust of the argument).