When was Christianity introduced in Scandinavia?
Church of Sweden
While some Swedish areas had Christian minorities in the 9th century, Sweden was, because of its geographical location in northernmost Europe, not Christianized until around AD 1000, around the same time as the other Nordic countries, when the Swedish King Olof was baptized. This left only a modest gap between the Christianization of Scandinavia and the Great Schism, however there are some Scandinavian/Swedish saints who are venerated eagerly by many Orthodox Christians, such as St. Olaf. However, Norse paganism and other pre-Christian religious systems survived in the territory of what is now Sweden later than that; for instance the important religious center known as the Temple at Uppsala at Gamla Uppsala was evidently still in use in the late 11th century, while there was little effort to introduce the Sami of Lapland to Christianity until considerably after that.
Religion in Iceland
The adoption of Christianity—which then was still identical to the Catholic Church—as the state religion ("kristnitaka", literally the "taking of Christianity"), and therefore the formal conversion of the entire population, was decided by the Althing in 999/1000, pushed by the king of Norway, Olaf Tryggvason. In that year, Christianity was still a minority in Iceland, while the belief in the Germanic religion was strong. However, some Christians had acquired high positions in the "goðorð" system and therefore considerable power in the Althing.