It would be a mistake to imagine that the dethronement of Our Lord began at the end of the 18th Century with the promulgation by the French Revolutionaries of the so-called "Rights of Man." 

The process began four centuries earlier, in 14th-century Italy, during what has become known as the "Renaissance." The word is French and means "rebirth." It refers to the rebirth of classical studies which began in Italy in the 14th Century. Those engaged in these studies were known as "humanists" because their studies were concerned with purely human topics, whereas in Europe, until that time, God had been the focus for almost every aspect of scholarship and art. Music, architecture, literature, painting, drama, philosophy, cosmology and, above all, theology ----- the Queen of the Sciences ----- were centered upon the Creator, and the Creator-creature relationship was axiomatic to every aspect of human thought.

Initially, there was no conflict between Humanism and the Church. Many humanists were also ecclesiastics. But as time passed, it became clear that the movement was tending to relegate religion to a place where it had little or no influence on human thought or human behavior; This tendency was implicit rather than explicit. It gave rise to the attitude that whereas faith is valid in its own domain, reason should be concerned only with what is scientifically demonstrable. The Creator-creature relationship was not formally denied, but attention became focused almost exclusively on man, to the neglect of God, who was, effectively, confined to the sacristy. Man was seen as an autonomous being, the focus of truth in a world of which he was master and which he had the ability to subdue and perfect, a being capable of building an earthly paradise by his own efforts, a utopia. The extent to which these ideas were reflected in the principles of the French Revolution, and later in atheistic Communism, hardly needs pointing out.

The practical result of Humanism was the divinization of man. The more God was diminished, the more man exalted himself and became his own God. In his book Christian Humanism Professor Thomas Molnar provides us with the following definition: 

"Humanism was a doctrine, or network of doctrines, putting man in place of God, and endowing him with features that he was inevitably to abuse." [1]

  I have mentioned the extent to which the principles of Humanism reached their logical conclusion in the French Revolution and in Communism, but the Protestant Reformation cannot be exempted from this charge. Our Lord Jesus Christ founded a visible 
Church, His Mystical Body, to continue His mission in the world until He comes again in glory. This Church was endowed with a visible head, the Bishop of Rome, the Vicar of Jesus Christ. A vicar is a person who is authorized to perform a function on behalf of another, as his officially designated deputy.

The Bishop of Rome has the authority to teach infallibly the true meaning of the Scriptures as intended by their Divine Author. The Protestant Reformers repudiated the authority of the Vicar of Christ, and hence the authority of Christ Himself. They claimed to accept the authority of the Scriptures, but the inevitable logic of Protestantism is that they accept the authority of Scripture as each individual Protestant interprets it. In other words, every Protestant makes his own reason his ultimate authority in religious matters. It has often been said that, in the final analysis, every Protestant is his own pope. We can go further still and state that in the final analysis Protestantism makes each Protestant into his own god. This is Humanism with a vengeance.

Catholics did not, of course, remain free from these influences, and in 1907, in the fifth year of his pontificate, Pope St. Pius X felt obliged to promulgate his encyclical letter Pascendi Dominici Gregis, condemning the errors of that Protestantized version of Catholicism known as Modernism, the ultimate logic of which, explained the Pope, was atheism. The most deplorable example of man's self-deification in our day is man's arrogation to himself of God's supreme and most fundamental authority, that is, His authority over life and death.

"I," says contemporary man, "shall decide for myself when a new human life shall begin and, once it has begun, whether it shall continue or be terminated. I shall use contraception to ensure that no new life is conceived without my consent, and, should a conception take place that I deem inconvenient, I shall terminate it by abortion." The next step in this diabolical process will be the legalization of euthanasia.

Although I have said that it would be a mistake to imagine that the dethronement of Christ the King was inaugurated by the promulgation of the French Revolution's Declaration of the Rights of Man, there can be no doubt that this Declaration constituted the first formal repudiation of Our Lord's Social Kingship, and that it was the most influential act in the process of securing His virtually universal dethronement during the next two centuries.

Before examining the extent to which this Declaration constituted a repudiation of Catholic teaching on the authority of the State, it is necessary to have a clear grasp of the content of this teaching. The doctrine of the Popes on the authority of the State is clear and self-evident to those with a proper understanding of the Creator-creature relationship, which is fundamental to a well-ordered society.

         THE CHURCH AND DEMOCRACY

A state is composed of two elements: the government, or those who govern, and the governed, authority being vested in those who govern. The Church is not committed to any particular form of government, and despite the tendency of Popes to refer to "princes" in their encyclicals, they were in no way opposed to democracy, if all that is meant by this term is that those who govern are chosen by a vote [based on either limited or universal suffrage]. What the Popes maintain, logically and uncompromisingly, is that the source of authority is precisely the same in an absolute monarchy, such as that of Louis XIV in 18th-century France, as in a country where the government is chosen in a democratic election in which every citizen has the right to vote, such as the United States today. In either situation papal teaching on the source of authority is clear and has already been stated: Omnis potestas a Deo. ----- "All authority comes from God." Pope Leo XIII explained in his encyclical Immortale Dei that:

Every civilized community must have a ruling authority, and this authority, no less than society itself, has its source in nature, and has, consequently, God for its author. Hence it follows that all public power must proceed from God. FOR GOD ALONE IS THE TRUE AND SUPREME LORD OF THE WORLD. Everything without exception must be subject to Him, and must serve Him, so that whosoever holds the right to govern, holds it from one sole and single source, namely, God, the Sovereign Ruler of all. "There is no power but from God."  [Rom. 13:1].

"There is no power but from God." This quotation from Romans 13: 1 states all that needs to be stated concerning the source of authority. Because those who govern derive their authority from God, and govern as His legates, and not as holding their authority from the people, no government can have a true right to enact any legislation contrary to the law of God, even if such legislation is the manifest wish of the majority of the people. The Church is totally opposed to any concept of democracy in which authority is said to reside in the people and in which those who govern are said to receive their authority from the people. Pope Leo XIII insisted in lmmortale Dei that:

In a society grounded upon such maxims, all government is nothing more nor less than the will of the people; and the people, being under the power of itself alone, is alone its own ruler . . .The authority of God is passed over in silence, just as if there were no God; or as if He cared nothing for human society; or as if men, in their individual capacity or bound together in social relations, owed nothing to God; or as if there could be a government of which the whole origin and power and authority did not reside in God Himself: Thus, as is evident, a state becomes nothing but a multitude, which is its own master and ruler.

www.catholictradition.org/Christ/christ-king1b.htm