A state religion (also called religious state or official religion) is a religion or creed officially endorsed by a sovereign state. A state with an official religion (also known as confessional state), while not secular, is not necessarily a theocracy. State religions are official or government-sanctioned establishments of a religion, but the state does not need to be under the control of the religion (as in a theocracy) nor is the state-sanctioned religion necessarily under the control of the state.
Official religions have been known throughout human history in almost all types of cultures, reaching into the Ancient Near East and prehistory. The relation of religious cult and the state was discussed by the ancient Latin scholar Marcus Terentius Varro, under the term of theologia civilis (lit. 'civic theology'). The first state-sponsored Christian church was the Armenian Apostolic Church, established in 301 CE. In Christianity, as the term church is typically applied to a place of worship for Christians or organizations incorporating such ones, the term state church is associated with Christianity as sanctioned by the government, historically the state church of the Roman Empire in the last centuries of the Empire's existence, and is sometimes used to denote a specific modern national branch of Christianity. Closely related to state churches are ecclesiae, which are similar but carry a more minor connotation.
In the Middle East, the majority of states with a predominantly Muslim population have Islam as their official religion, though the degree of religious restrictions on citizens' everyday lives varies by country. Rulers of Saudi Arabia use both secular and religious power, while Iran's secular presidents are supposed to follow the decisions of religious authorities since the 1979 Islamic Revolution. Turkey, which also has Muslim-majority population, became a secular country after Atatürk's Reforms, although unlike the Russian Revolution of the same time period, it did not result in the adoption of state atheism.
The degree to which an official national religion is imposed upon citizens by the state in contemporary society varies considerably; from high as in Saudi Arabia and Iran to minimal or none at all as Denmark, England, Iceland, and Greece.
2. But there is yet another error no less pernicious to the well-being of the nations and to the prosperity of that great human society which gathers together and embraces within its confines all races. It is the error contained in those ideas which do not hesitate to divorce civil authority from every kind of dependence upon the Supreme Being -- First Source and absolute Master of man and of society -- and from every restraint of a Higher Law derived from God as from its First Source. Thus they accord the civil authority an unrestricted field of action that is at the mercy of the changeful tide of human will, or of the dictates of casual historical claims, and of the interests of a few. Once the authority of God and the sway of His law are denied in this way, the civil authority as an inevitable result tends to attribute to itself that absolute autonomy which belongs exclusively to the Supreme Maker. It puts itself in the place of the Almighty and elevates the State or group into the last end of life, the supreme criterion of the moral and juridical order, and therefore forbids every appeal to the principles of natural reason and of the Christian conscience. We do not, of course, fail to recognize that, fortunately, false principles do not always exercise their full influence, especially when age-old Christian traditions, on which the peoples have been nurtured, remain still deeply, even if unconsciously, rooted in their hearts.
The idea which credits the State with unlimited authority is not simply an error harmful to the internal life of nations, to their prosperity, and to the larger and well-ordered increase in their well-being, but likewise it injures the relations between peoples, for it breaks the unity of supra-national society, robs the law of nations of its foundation and vigor, leads to violation of others' rights and impedes agreement and peaceful intercourse. Now no one can fail to see how the claim to absolute autonomy for the State stands in open opposition to this natural way that is inherent in man (nay, denies it utterly) and therefore leaves the stability of international relations at the mercy of the will of rulers, while it destroys the possibility of true union and fruitful collaboration directed to the general good. (Papal Encyclical, Summi Pontificatus, 20 October 1939).
3. An error of modernism identifed by the belief that: The Church ought to be separated from the State, and the State from the Church. (Papal Allocution, Acerbissimum, 27 September 1852).
4. An error of modernism identifed by the belief that: In the present day it is no longer expedient that the Catholic religion should be held as the only religion of the State, to the exclusion of all other forms of worship. (Papal Allocution, Nemo Vestrum, 26 July 1855).
5. And, since where religion has been removed from civil society, and the doctrine and authority of divine revelation repudiated, the genuine notion itself of justice and human right is darkened and lost, and the place of true justice and legitimate right is supplied by material force, thence it appears why it is that some, utterly neglecting and disregarding the surest principles of sound reason, dare to proclaim that "the people's will, manifested by what is called public opinion or in some other way, constitutes a supreme law, free from all divine and human control; and that in the political order accomplished facts, from the very circumstance that they are accomplished, have the force of right." But who, does not see and clearly perceive that human society, when set loose from the bonds of religion and true justice, can have, in truth, no other end than the purpose of obtaining and amassing wealth, and that (society under such circumstances) follows no other law in its actions, except the unchastened desire of ministering to its own pleasure and interests? (Papal Encyclical, Condemning Current Errors: Quanta Cura, 8 December 1986).