Christianity originated in what is now the country of Israel. Jesus Christ hailed from the town of Nazareth in the region of Galilee, and much of his early ministry took place in that area.
At the time of Jesus' birth and ministry, Galilee was ruled by Herod Antipas, one of the four Judean tetrarchs who were installed after the death of Herod the Great. Galilee was a client state of the Roman Empire that was technically autonomous but functioned under the thumb of the Roman emperor. At first, Christianity stayed in Galilee and the other four tetrarchies, but it eventually spread throughout the Mediterranean world and beyond.