Picture non-Christian Europe in 850: The Scandinavian countries and their Vikings, ravaging everything from Ireland to Russia. Saracen Muslims pushing into southern Italy, even sacking Rome. Magyars invading central Europe before finally conquering and settling in what we know as Hungary. Poland, much of the Slavic countries (e.g., Czeck Republic), the Baltic, and Russia . . . all non-Christian.
This all changed: Poland (866), Today’s Slavic countries (Moravia) through Cyril and Methodius (870s), Denmark and Norway (960s), Russia (988), Hungary, with the fierce Magyars (late 900s, but concretely Christian by 1000). Sweden was a little slow, but by Christian influence clearly felt by 900s and it was a Christian nation by 1050. (Baltics held out for another two hundred years.)
Europe by 1000 was Christian, stretching from Ireland to Russia, from Oslo to Palermo in Sicily, from the Kingdom of Leon in today’s northern Portugal through present day Turkey. The only exceptions: southern Spain and the backwards Baltic.