Christianity had no influence in early Europe.
Nearly 300 years after the death of Jesus Christ, the religion based on his teachings remained a small sect of the Roman Empire, practiced alongside many other faiths, including monotheism and polytheism. Certain aspects of Christianity, such as its egalitarian nature, made the imperial authorities suspicious, however, Christians were regularly persecuted.
Throughout the ancient world, changes in social, political, and economic conditions were reflected in cultural and religious changes; Christianity was just one of many of the monotheisms that had prevailed in the Roman Empire, including Mithraism in Persia, and they had much in common.
At that time, the scholar class preferred to promote polytheism and make the people believe that there were many gods and heroes in the world, so that they could accept that there were other ruling classes under the emperor.
At that time, Christian doctrine was just a collection of stories about the search for psychological comfort among the poor: God's messengers were also suffering, so it was normal for "me" to suffer.
It was not until the Roman Emperor Constantine formally established Christianity as the state religion that the teachings of Christianity really spread.
By 285, the Roman Empire had been divided into two halves, east and west, ruled by Constantine and Maxentius, respectively.
In October 312, Emperor Constantine's army was stationed at the Milvian Bridge near Rome, preparing for the Battle of Maximius, The Western Roman Emperor.
Traditionally, before they met, Constantine dreamed of a burning cross in the sky with the word "conquest" inscribed on it. This convinced him that he had the support of the Christian God. With this belief, his army continued to win victories.
In fact, in order to legitimize his ambition to become the sole emperor, Constantine seems to have been looking for theological "support."
The Christian God was not the first God that Constantine believed in; his earlier versions involved the Greek and Roman god of Apollo. Monotheistic Christianity was a good choice for him than Greco-Roman polytheism: there was only one god in heaven and only one emperor on earth.
Although the legend of Constantine's revelation was sudden, the army was suddenly dreamed of. But his conversion to Christianity was gradual—he was not baptized until his deathbed many years later.
However, shortly after his victory at the Milvian Bridge, he began the process of reviving Christianity, which was subsequently elevated;
In 331 AD, he issued the Edict of Milan, proclaiming religious tolerance for Christianity within the Roman Empire. It was also this edict that allowed Christianity to truly spread in large quantities in the world.
In 324 AD, Constantine deposed the emperor in the East, became the sole ruler of the Roman Empire, and tried to use Christianity to unify his complex and uncontrollable empire.
To make the increasingly dominant eastern half easier to administer, he built a new city called Constantinople (present-day Istanbul) and sanctified it with Christian and pagan rituals, but only allowed the construction of Christian churches.
Although it took a while for all Roman citizens to convert to Christianity, during the reign of Constantine, the upper echelons of society flocked to the church in search of political progress and the personal favor of the emperor.
Christianity was not a single, unified religion at the time, but had many doctrinal divisions.
In 325 AD, Constantine convened the first universal Christian conference, the Council of Nicea, primarily to resolve the Arian divisions, a theological debate over whether Jesus had the same essence as God.
After reunification, the people received a more direct and explicit religious education in the churches of the new city, and the society was united.
As the Roman Empire adopted and molded the church as an instrument of social and political control, unity, and stability, this belief grew increasingly connected to the empire.
In the mid-300s AD, the ancient Emperor Julian tried to revive paganism, but it was too late; Christians had become the majority, at least in the Eastern Empire.
Under the reign of Theodosius I (reigned 379-395), pagan temples and cults were suppressed, heresy was outlawed, and Christianity became the official religion of the Roman Empire.
Eventually, it also became the faith of the barbarian successor states of the Western Roman Empire and the Eastern Byzantine Empire.
In the many centuries that followed, the churches of the Western Empire (Catholic) and the Eastern Empire (Orthodox) were gradually divided in doctrine and organization, but Christianity remained.