All the cultures had one thing in common: Christianity.
Chesterton, with the example of Ireland before him, wouldn’t really count on that as a unifier.
But it was not any form of what passes for Christianity, as is the case now:
Alexis de Tocqueville (1805—1859. French Catholic political thinker and historian; best known for his two volume, “Democracy in America”) — The sects that exist in the United States are innumerable. They all differ in respect to the worship which is due to the Creator; but they all agree in respect to the duties which are due from man to man. Each sect adores the Deity in its own peculiar manner, but all sects preach the same moral law in the name of God...Moreover, all the sects of the United States are comprised within the great unity of Christianity, and Christian morality is everywhere the same...
In the United States the sovereign authority is religious, and consequently hypocrisy must be common; but there is no country in the whole world in which the Christian religion retains a greater influence over the souls of men than in America, and there can be no greater proof of its utility, and of its conformity to human nature, than that its influence is most powerfully felt over the most enlightened and free nation of the earth...
There is certainly no country in the world where the tie of marriage is more respected than in America or where conjugal happiness is more highly or worthily appreciated, In Europe almost all the disturbances of society arise from the irregularities of domestic life. To despise the natural bonds and legitimate pleasures of home is to contract a taste for excesses, a restlessness of heart, and fluctuating desires. Agitated by the tumultuous passions that frequently disturb his dwelling, the European is galled by the obedience which the legislative powers of the state exact. But when the American retires from the turmoil of public life to the bosom of his family, he finds in it the image of order and of peace...
The Americans combine the notions of Christianity and of liberty so intimately in their minds, that it is impossible to make them conceive the one without the other; and with them this conviction does not spring from that barren traditionary faith which seems to vegetate in the soul rather than to live...
Thus religious zeal is perpetually warmed in the United States by the fires of patriotism. These men do not act exclusively from a consideration of a future life; eternity is only one motive of their devotion to the cause. If you converse with these missionaries of Christian civilization, you will be surprised to hear them speak so often of the goods of this world, and to meet a politician where you expected to find a priest.
They will tell you that "all the American republics are collectively involved with each other; if the republics of the West were to fall into anarchy, or to be mastered by a despot, the republican institutions which now flourish upon the shores of the Atlantic Ocean would be in great peril. It is therefore our interest that the new states should be religious, in order that they may permit us to remain free." (Democracy in America, Volume I Chapter XVII, 1835; http://xroads.virginia.edu/~HYPER/DETOC/religion/ch1_17.htm)
• There are certain populations in Europe whose unbelief is only equaled by their ignorance and their debasement, while in America one of the freest and most enlightened nations in the world fulfills all the outward duties of religion with fervor.
Upon 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 did I perceive the great political consequences resulting from this state of things, to which I was unaccustomed. In France I had almost always seen the spirit of religion and the spirit of freedom pursuing courses diametrically opposed to each other; but in America I found that they were intimately united, and that they reigned in common over the same country. (Democracy in America, [New York: A. S. Barnes & Co., 1851), pp. 331, 332, 335, 336-7, 337; http://xroads.virginia.edu/~HYPER/DETOC/religion/ch1_17.htm)
And the Divine Being seems to have manifested His approbation of the mutual forbearance and kindness by which the different sects treat each other, and by the remarkable prosperity with which He has been please to favor the whole country. (Benjamin Franklin, "Information to those who would Remove to America" In Franklin, Benjamin. The Bagatelles from Passy. Ed. Lopez, Claude A. New York: Eakins Press. 1967; http://mith.umd.edu//eada/html/display.php?docs=franklin_bagatelle4.xml. Also, John Gould Curtis, American history told by contemporaries .... Volume 3, p. 26)