Marxism was supposed to be a synthesis of German philosophy, French politics, and English economics. The list of ingredients for mainstream Christianity is the Jewish prophetic tradition, Greek philosophy, and Roman politics, but mostly Roman politics. The crucial moment in the evolution of the religion was not the crucifixion, but Constantine’s religio-political coup. Before Constantine, the various Christian groups represented a challenge to the unity of an Empire that had come to insist on an ideological conformity alien to the traditional tolerance of pagan societies. Adopting—and adapting—Christianity as the state religion resolved this conflict. But what triumphed was quite distinct from the Christianity of the sects. It was a chimera that combined some of the elements of the old faith with the persecuting machinery of the Roman state. Many people have pointed out that the theological mysteries defined as orthodoxy at Nicaea and other early councils were simply frozen political compromises; but the true mysterium was not that Christ was all man and all god, but that the faith would henceforth be simultaneously all spirituality and all politics.
Christianity was merely a large minority before the emperors began to patronize it. The emperors made Europe Christian, not only by directly imposing the religion on the Romans but by providing an example to the princes that created the new states in barbarian lands. While individuals were certainly susceptible to the appeal of the new faith, the wholesale conversion of the pagans was accomplished from above by ambitious kings when it wasn’t simply enforced at the point of Frankish swords. The one exception I’m aware of is Medieval Iceland, where there were no kings; but even there the decision to convert to Christianity was made for overtly political reasons at a memorable meeting of the Althing in the year 1000.