You are right. It all started to happen in the 16th century. Before that there was not denominations; there was one, holy, catholic and apostolic church.
BTTT for the truth!
Oh, you must know that is not true today nor was up to the in the 16th century .
The church of Rome is basically invisible in the NT, and the largest deformation of it, though it retains enough Truth whereby a relative few souls within it may actually come to Christ as damned and destitute sinners, casting all their faith upon the risen Son of God to save them by His sinless shed blood, and which is my prayer.
And RCs today are overall liberal (at least in the West) and less unified in basic values and many core truths than evangelicals, while Rome treats even proabortion, prohomo, promuslim pols as members in life and in death, and a near majority which support such, which partly evidences what Rome really believes (Ja. 2:18; Mt. 7:20) and is more substantial and speaks louder than some paper conservative statements.
In addition, Catholicism exists in formal sects and schisms, the latter including the EOs who substantially differ with Rome.
Which goes back quite a way.
There is a claim that "the church was unified under the pope until 1054". But there was a "schism" centuries earlier than that, which is a far larger and messier divide than the 1054 schism between the Roman and Orthodox churches. It makes a lie of the "unified under the pope" claims of today's Roman Catholic apologists....
The churches in Asia, "the churches of the east", which had no idea that there was a "Petrine ministry" for many centuries, had as much of a claim to "apostolic succession" as did any of the European churches, and which grew far larger than any of the churches in Europe, before being snuffed out by Islam -- not in the 6th or 7th centuries, but the 12th and 13th centuries, likely a response to (a) the Mongol invasions (which were favorable to Christianity), and (b) the Crusades. (Not saying there were no massacres prior to the Crusades. But the Crusades exacerbated a bad situation).
Here are a couple of works overviewing these "Churches of the East":
Samuel Hugh Moffett: "A History of Christianity in Asia"
Philip Jenkins: The Lost History of Christianity
Mar Bawai Soro: The Church of the East: Apostolic and Orthodox
Here is how Moffett describes this "Great Schism" of the 5th century:
What finally divided the early church, East from West, Asia from Europe, was neither war nor persecution, but the blight of a violent theological controversy, that raged through the Mediterranean world in the second quarter of the fifth century. It came to be called the Nestorian controversy, and how much of it was theological and how much political is still being debated, but it irreversibly split the church not only east and west but also north and south and cracked it into so many pieces that it was never the same again. Out of it came an ill-fitting name for the church in non-Roman Asia, "Nestorian."
Of course, Nestorius was accused of things (by Cyril) that he never espoused. Moffett also goes into a good bit of detail about this. More .
And then you have the unity of the church of Rome leading up to the Reformation:
Referring to the schism of the 14th and 15th centuries, Cardinal Ratzinger observed,
"For nearly half a century, the Church was split into two or three obediences that excommunicated one another, so that every Catholic lived under excommunication by one pope or another, and, in the last analysis, no one could say with certainty which of the contenders had right on his side. The Church no longer offered certainty of salvation; she had become questionable in her whole objective form--the true Church, the true pledge of salvation, had to be sought outside the institution. "It is against this background of a profoundly shaken ecclesial consciousness that we are to understand that Luther, in the conflict between his search for salvation and the tradition of the Church, ultimately came to experience the Church, not as the guarantor, but as the adversary of salvation. (Joseph Cardinal Ratzinger, head of the Sacred Congregation of the Doctrine of the Faith for the Church of Rome, “Principles of Catholic Theology,” trans. by Sister Mary Frances McCarthy, S.N.D. (San Francisco: Ignatius, 1989) p.196). http://www.whitehorseinn.org/blog/2012/06/13/whos-in-charge-here-the-illusions-of-church-infallibility/) Cardinal Bellarmine: "Some years before the rise of the Lutheran and Calvinistic heresy, according to the testimony of those who were then alive, there was almost an entire abandonment of equity in ecclesiastical judgments; in morals, no discipline; in sacred literature, no erudition; in divine things, no reverence; religion was almost extinct. (Concio XXVIII. Opp. Vi. 296- Colon 1617, in “A History of the Articles of Religion,” by Charles Hardwick, Cp. 1, p. 10,) Catholic historian Paul Johnson additionally described the existing social situation among the clergy at the time of the Reformation: “Probably as many as half the men in orders had ‘wives’ and families. Behind all the New Learning and the theological debates, clerical celibacy was, in its own way, the biggest single issue at the Reformation. It was a great social problem and, other factors being equal, it tended to tip the balance in favour of reform. As a rule, the only hope for a child of a priest was to go into the Church himself, thus unwillingly or with no great enthusiasm, taking vows which he might subsequently regret: the evil tended to perpetuate itself.” (History of Christianity, pgs 269-270)
Well, except for the Eastern Orthodox Church, the Syrian Church, the Coptic Church, the Ethiopian Church, the Assyrian Church, the Armenian Church, and all the various Indian churches . . . every one of which can trace itself back to the original apostles.
I don't really have a dog in this fight, but it burns my biscuits when Catholics pretend there were no rival claimants to being the "one true church" prior to the sixteenth century.