By the way: even in the first century, Christianity was hardly a unified, monolithic movement - and first conflicts over who got to claim the title of TRUE Christianity are even recorded in the Bible.
Take, for example, the conflict between the "Judaizers" of the Jerusalem Church and its Three Pillars and Paul's faction. Even if the conflict was as smoothly resolved as the author of Luke-Acts wants us to believe (in sharp contrast to some passages within the Pauline epistles that suggest an ongoing rivalry between the two sects), it's still a doctrinal split.
By the time one faction gained undisputed ascendancy, the face of Christianity had already changed significantly - in spite of what the Orthodox like to believe.