Rome has always sought the union of church and state. The separation of these two was one of the most fundamental issues that founded America. As Steve Mount's website on American politics tells us, "The Bill of Rights protects a lot of other freedoms. For example, you can believe in any religion you want. The government cannot force you to believe in something."ⁱ Read also the First Amendment of the US Constitution

Here are several sources discussing the political Church of Rome:

The fact is that very few Protestants have realized how entirely Rome is a political church, and that she always makes her political advancement her first object.

It must be remembered, however, that the Pax Romana was enforced, not by resolutions of an Amphictyonic Councilor of any representative body whatsoever, but by the will of an emperor and the swords of his soldiers. The Roman Empire was constructed by conquest and subjugation, not by any self-determination of peoples; and the peace which it enshrined was not a democratic peace.

The Holy Roman Empire and the Catholic Church.
Upon posterity the political influence of Imperial Rome was much greater than was that of separatist Greece. The idea of preserving unity among civilized men, of promoting universal allegiance to a common lawgiver and obedience to a common law, appealed powerfully to thoughtful men throughout the "Dark" and "Middle" Ages, and has continued to affect mankind to the present moment. This idea found expression from the eighth to the seventeenth centuries in the efforts of various ambitious warriors and statesmen of western Europe to build world empires that could be called Roman - Charlemagne, Otto, the Hohenstaufens, and the Hapsburgs.

The same idea likewise found expression, perhaps more real, in the Roman Church, which, in the political as well as in the strictly religious domain, long performed many of the services which had contributed to the grandeur of Rome; the medieval church tamed and trained the barbarians, developed a system of private and public law, and in converting Germans and Poles and Scandinavians and English and Hungarians and Czecho-Slovaks, as well as Mediterranean folk, to a common cult and to common ideals, laid claim to a universal dominion.

Disregarding the maxims and the spirit of the Gospel, the papal Church, arming herself with the power of the sword, vexed the Church of God and wasted it for several centuries, a period most appropriately termed in history, the "dark ages".  The kings of the earth gave their power to the "Beast."

The union of the Church with the State renders persecution possible; and hitherto churches have not been slow to avail themselves of the secular arm that they might confound all dissent with arguments which come home to the bone and the flesh [flogging, torture, and execution].  All churches, when they lose the spirit of Christ, are very prone to persecute; but a horrible pre-eminence must be awarded to the scarlet harlot of the seven hills [i.e., the Vatican], for no church on earth except that of Rome has had a separate institution [i.e., the Office of Inquisition] for hunting out and destroying heretics...

Long pampered by the State, she came to be its lord and tyrant, using fire and sword, prison and rack, to work her accursed will. The Inquisition was the masterpiece of infernal craft and malice, and its deeds were far more worthy of fiends than men. If the church of Rome could at this moment change its Ethiopian skin forever, lay aside its leopard’s spots, and become a pure community, ten thousand years of immaculate holiness and self-denying philanthropy could not avail to blot out the remembrance of the enormous crimes with which the Inquisition has loaded it. There is a deep and indelible sentence of damnation written upon the apostate church by avenging justice for its more than infernal cruelties, and the curse is registered in heaven; nor can any pretences to present liberality reverse the condemnation which outraged humanity has pronounced against it; its infamy is engraven in the rock forever. Centuries of the most liberal policy would not convince mankind that Popery had become tolerant at heart; she wallowed so greedily in oppression, torture, and murder in her palmy [i.e., flourishing] days, that the foam of human gore hangs around her wolfish fangs, and men will not believe her to be a gentle lamb, let her ‘bleat’ as she may...

Rome [i.e., the Vatican] made the worst possible use of the weapon which the State gave her, but the radical evil was the State’s entering into alliance with the Church, and lending its power to fulfill her purposes.  Had true church principles prevailed, the crimes which make us shudder would have been impossible.  Disarm and dis-establish every sect, and leave each religion to its own moral and spiritual power, and no inquisition can be dreamed of; but put forward the doctrine that a state should propagate or maintain religion, and you have uncaged the ‘lion’; no one knows how much he may rend and devour...

To prevent forever the possibility of Papists roasting Protestants, Anglicans hanging Romish priests, and Puritans flogging Quakers, let every form of state-churchism be utterly abolished, and the remembrance of the long curse which it has cast upon the world be blotted out forever.

When governments submitted their powers to the control of Rome, joining Church and State, the Dark Ages were ushered in. But alliance of State and Church occurred not only hundreds of years ago, but it also in the 1940s. The Croatian State combined with the hierarchy of the Roman Catholic Church to carry out savage religious genocide against innocent Serb Orthodox Christian men, women, elderly, and children—torturing and murdering over 600,000 people in a modern-day Inquisition.