Immediately the Day of Pentecost came the gospel exploded into the nations, fulfilling the Old Testament prophecies about the reign of Christ over all flesh. By the end of the first millennium AD the church in the East was twice as large as the church in the West. Archaeology shows that the main portion of humanity was at least in proximity to the gospel in the first millennium. (America or Australia is not studied here, in respect to actual population levels, or the possibility of gospel penetration in the first millennium.)
It is evident that by the end of the 1st Century AD the gospel had reached Africa, Russia, the Middle East, Asia, India and Europe as far as Britain. The gospel strengthened rapidly in these regions in the years that followed. By the 700’s Christianity had a strong presence in much of China and was in Japan, Indonesia and the Philippines.
These studies are supported archeologically, not by tradition. For an introduction see Samuel Moffett, A History of Christianity in Asia and search Martin Palmer, P.Y. Saeki, John Stewart and John England on the Internet.
It is helpful to ask why missions in some of these earlier reached regions eventually failed and they became largely lost to the gospel. It is helpful also to see how the early church succeeded so rapidly in the midst of strong persecution and heresy. Jesus said, “I will build My church and the gates of hell will not prevail against it.” (Matt 16:18).
The Book of Acts
Acts records the expansion of Christianity to the West. It was written by Luke who worked with the Apostle Paul. Paul worked west of Jerusalem, as far as Spain. Acts says very little about other missions that were obviously going on concurrently with Paul’s.
For example, the Magi came from the east (Persia) when Jesus was born (Matt 2:1). Persia is modern day Iran. Magi were not kings, but wise men, or scientists/astrologers. They took the gospel back to Persia. An African also carried Jesus’ cross.
On the Day of Pentecost men were present from “every nation under heaven” (Acts 2:5). These included Iranians and Russians and those from Elam, east of the Persian Gulf. These also took the gospel back with them.
In 37AD the church at Jerusalem was scattered in the early persecutions (Acts 8:1). Believers travelled out preaching the gospel everywhere. These at first preached to the Jews only and the largest Jewish community then was in Babylon. These believers would have gone to many places not mentioned in Acts.
In Acts 8 Philip spoke to the eunuch who served the Queen of Ethiopia. The eunuch took the gospel back to Ethiopia. Ethiopia then was a more general notation for the sub-Sahara races, not just limited to the Ethiopia of today. Asians and an African were present at the first church council in Acts 15. There were many other outreaches the Holy Spirit was undertaking that we know very little, if anything, about.