I have always heard that Iceland was originally settled by Vikings, who I imagine where pagans, and that Greenland was eventually colonized by similar Vikings. Did the relative isolation of both these places have any effect on how Christianity spread to them? Was there any great missionaries that helped in the converting endeavor? Could there have been any Christians that helped with the colonization of Newfoundland?
Iceland was first settled in 874, it was Christianized in year 1000. How that went about was that Icelanders agreed to officially recognize Catholicism as their religion yet they could worship pagan gods in private. The actual conversion of Icelanders went a lot slower and no real efforts were made for the first few generations of Christianity to teach about Catholicism. It took roughly about 200 years for Icelanders to convert completely to Catholicism, since Pagan worship was all done in private it's difficult to make a clear estimate though. But Paganism was never truly gone from Iceland, there's an Icelandic grimoire from the 17th century that refers heavily to the Norse gods and how people could call upon them for help. Because of isolation and minimal interference from the Vatican, paganism was prominent in society for longer in Iceland than Scandinavia, definitely.