Alexis de Tocqueville was a French historian, political theorist, and author, who became famous for his insightful study of American democracy. He travelled through the US in the early 1830s, recording the details of American society.  Tocqueville used these in his Democracy in America (1835-1840). A liberal, Tocqueville championed democracy and popular sovereignty.  Yet he also offered compelling critiques of democratic societies.  

Selection from Alexis de Tocqueville, Democracy In America, Chapter XVII (1835-1840). Excerpted from the University of Virginia's Alexis de Tocqueville and Religion

…THE philosophers of the eighteenth century explained in a very simple manner the gradual decay of religious faith. Religious zeal, said they, must necessarily fail the more generally liberty is established and knowledge diffused. Unfortunately, the facts by no means accord with their theory. There are certain populations in Europe whose unbelief is only equaled by their ignorance and debasement; while in America, one of the freest and most enlightened nations in the world, the people fulfill with fervor all the outward duties of religion. 

On my arrival in the United States the religious aspect of the country was the first thing that struck my attention; and the longer I stayed there, the more I perceived the great political consequences resulting from this new state of things. In France I had almost always seen the spirit of religion and the spirit of freedom marching in opposite directions. But in America I found they were intimately united and that they reigned in common over the same country. My desire to discover the causes of this phenomenon increased from day to day. In order to satisfy it I questioned the members of all the different sects; I sought especially the society of the clergy, who are the depositaries of the different creeds and are especially interested in their duration. As a member of the Roman Catholic Church, I was more particularly brought into contact with several of its priests, with whom I became intimately acquainted. To each of these men I expressed my astonishment and explained my doubts. I found that they differed upon matters of detail alone, and that they all attributed the peaceful dominion of religion in their country mainly to the separation of church and state. I do not hesitate to affirm that during my stay in America I did not meet a single individual, of the clergy or the laity, who was not of the same opinion on this point. . . 

In proportion as a nation assumes a democratic condition of society and as communities display democratic propensities, it becomes more and more dangerous to connect religion with political institutions; for the time is coming when authority will be bandied from hand to hand, when political theories will succeed one another, and when men, laws, and constitutions will disappear or be modified from day to day, and this not for a season only, but unceasingly. Agitation and mutability are inherent in the nature of democratic republics, just as stagnation and sleepiness are the law of absolute monarchies. . . . 

In America religion is perhaps less powerful than it has been at certain periods and among certain nations; but its influence is more lasting. It restricts itself to its own resources, but of these none can deprive it; its circle is limited, but it pervades it and holds it under undisputed control. 

On every side in Europe we hear voices complaining of the absence of religious faith and inquiring the means of restoring to religion some remnant of its former authority. It seems to me that we must first attentively consider what ought to be the natural state of men with regard to religion at the present time; and when we know what we have to hope and to fear, we may discern the end to which our efforts ought to be directed. . . 

In Europe, Christianity has been intimately united to the powers of the earth. Those powers are now in decay, and it is, as it were, buried under their ruins. The living body of religion has been bound down to the dead corpse of superannuated polity; cut but the bonds that restrain it, and it will rise once more. I do not know what could restore the Christian church of Europe to the energy of its earlier days; that power belongs to God alone; but it may be for human policy to leave to faith the full exercise of the strength which it still retains.