Judaea, at the beginning of the I Century AC was a small province, but with a complex structure, heir to the Hellenistic influence over the Jews after Alexander the Great conquered the Persian Empire, and then the Maccabean Revolt that created the Asmonean Kingdom, that would then be invaded by Pompey the Great in 40 BC.
As such, there were a heavily Hellenized area (the Decapolis) and Caesarea, places with large Greek populations, as well as the residence of the Roman officials. Then came Galilee, Idumea, Philistea and Judaea. Galilee, Idumea and Philistea were places ruled by the heirs of Herod the Great, client kings that however would not have the degree of authority as that of their father.
Lastly, Judaea was governed by the praetor (the office in charge of Pontius Pilatus) appointed directly by the emperor. In contrast to this, were also the religious divisions between pagans and Jews, and between Jews in the sects of pharisees, saducees, and esenians, with this sects battling for power in the Sanhedrin (the Council of the Temple) and to influence in the appointing of the Supreme Priest of the Temple.
This was the context in which Jesus lived and teached. And this context heavily influenced his teachings, specially in that he appealled to the proximity of the end of times, and the coming of a kingdom of Heaven that would be open to all the members of society. In this he clashed with the status quo, and will lead to his execution.
But it was at this point that Christianity began its evolution into a religion. In this, a great role was played by the Apostle Paul. It was Paul teachings, based upon the idea of opening the community to the "gentiles" (Greeks and Romans) in contrast to a more pure Jewish vision (the one of the Church in Jerusalem). The views of Paul would prove crucial after the Jewis Revolf of 66-70 AC that ended in the Siege of Jerusalem and the destruction of the Temple.
WIth this, Christians gradually evolved in a distinct cult from the Jews, and would evolve in the following two centuries to a more God-like view of Jesus and its assimilation into the figure of "Christ" (the chosen one, the savior). It's appeal grow in the population with the idea of the end of the world, the Kingdom of Heaven and salvation, This was explained due to the crisis scourging the Roman Empire, specifically the Third Century Crisis.
With this, and the progressive decline of paganism, aided in part due to the rise of the cult of Sol Invictus and Mitra (that created a more "monotheistic" view of religion) Christianity competed with this other cults, finally achieving supremacy after Constantine the Great unified the Empire. By then, Christians numbered almost a million followers, and was predominant in the great urban centers such as Antioch. Finally, Theodosius the Great make Christianity the official religion of the Empire, and practically banned paganism by 386.
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