I believe these quotes from the book Great Controversy by Ellen White answer you.
The apostle Paul, in his second letter to the Thessalonians, foretold the great apostasy which would result in the establishment of the papal power. He declared that the day of Christ should not come, "except there come a falling away first, and that man of sin be revealed, the son of perdition; who opposeth and exalteth himself above all that is called God, or that is worshiped; so that he as God sitteth in the temple of God, showing himself that he is God." And furthermore, the apostle warns his brethren that "the mystery of iniquity doth already work." 2 Thessalonians 2:3, 4, 7. Even at that early date he saw, creeping into the church, errors that would prepare the way for the development of the papacy.
Little by little, at first in stealth and silence, and then more openly as it increased in strength and gained control of the minds of men, "the mystery of iniquity" carried forward its deceptive and blasphemous work. Almost imperceptibly the customs of heathenism found their way into the Christian church. The spirit of compromise and conformity was restrained for a time by the fierce persecutions which the church endured under paganism. But as persecution ceased, and Christianity entered the courts and palaces of kings, she laid aside the humble simplicity of Christ and His apostles for the pomp and pride of pagan priests and rulers; and in place of the requirements of God,
she substituted human theories and traditions. The nominal conversion of Constantine, in the early part of the fourth century, caused great rejoicing; and the world, cloaked with a form of righteousness, walked into the church. Now the work of corruption rapidly progressed. Paganism, while appearing to be vanquished, became the conqueror. Her spirit controlled the church. Her doctrines, ceremonies, and superstitions were incorporated into the faith and worship of the professed followers of Christ.
This compromise between paganism and Christianity resulted in the development of "the man of sin" foretold in prophecy as opposing and exalting himself above God. That gigantic system of false religion is a masterpiece of Satan's power-a monument of his efforts to seat himself upon the throne to rule the earth according to his will.
The woman (Babylon) of Revelation 17 is described as "arrayed in purple and scarlet color, and decked with gold and precious stones and pearls, having a golden cup in her hand full of abominations and filthiness:...and upon her forehead was a name written, Mystery, Babylon the Great, the mother of harlots." Says the prophet: "I saw the woman drunk with the blood of the saints, and with the blood of the martyrs of Jesus."Babylon is further declared to be "that great city, which reigneth over the kings of the earth." Revelation 17:4-6, 18. The power that for so many centuries maintained despotic sway over the monarchs of Christendom is Rome. The purple and scarlet color, the gold and precious stones and pearls, vividly picture the magnificence and more than kingly pomp affected by the haughty see of Rome. And no other power could be so truly declared "drunken with the blood of the saints" as that church which has so cruelly persecuted the followers of Christ. Babylon is also charged with the sin of unlawful connection with "the kings of the earth." It was by departure from the Lord, and alliance with the heathen, that the Jewish church became a harlot; and Rome, corrupting herself in like manner by seeking the support of worldly powers, receives a like condemnation.
