It wasn't easy

Missions and Missionaries. The Christian Church has always depended on missions and missionaries for growth. The disciples of Jesus were the first Christian missionaries. Paul was sent to tell the Gentiles about Christianity. His work, and the work of others like him, brought the entire Roman Empire under Christian rule by the middle of the fourth century.
For the next thousand years, the Church sent missionaries to the barbarians of Northern and Eastern Europe who knew nothing of Jesus. Ufilas, an Arian bishop, brought Christianity to the Goths. St. Patrick was sent to Ireland, St. Columba carried the gospel to Scotland, and St. Augustine became England's first Archbishop of Canterbury. In Germany the brave Boniface cut down a sacred oak because it had long been a place of sacrifice to the god Thor. Ansgar was missionary to the Scandinavians, and Vladimir was a Christian leader among the Russian tribes.
As late as the 1200's, human sacrifices were still offered among Slavic tribes. [If there are dead bodies left over after your religious ceremony, your religion is satanic!] The people of Lapland and other far northern regions did not learn of Christian benefits until after the Protestant Reformation of the 1500's. But Christianity had reached China before the seventh century..." - From an old Encyclopedia