Christianity first emerged in the vicinity of Jerusalem ca. 33 AD following the crucifixion and resurrection of Jesus, believed by some Jews to be the Christ. After this, Christianity remained a small insignificant faith community in Judea, until the Missionary journeys of St. Paul. During these journeys ca. 40-50 AD the term "Christians" came into common use in Antioch in Syria (Not Antioch Greece), and Christianity became a common faith throughout the Roman Empire.
With the conversion of Emperor Constantine in 312 AD, and subsequent legalization of Christianity in the Empire, Christianity became a mainstream movement throughout all of Europe.
After the Empire fell, Christianity continued to spread through Europe as the "barbarians" began to become Christians. By 1492, the vast majority of Europeans were Christians. After Columbus' famous voyage, Christianity spread to the "New World" and continued to spread like wildfire.