One of the interesting questions for me is why did countries like Spain, Portugal and Ireland, which could in many way be considered Integralist, so rapidly secularise following the collapse of the political structures which supported the Church.
One of the brightest guys dealing with the subject is José Casanova, one of the world's top scholars on the sociology of religion. Cassanova's expertise is in the relation between religion, modernity and secularisation. I thought I would post an extended quote from one of his books as he provides a very good explanation with regard to the mechanics at play. For those of you who can't be bothered reading it the executive summary is as follows:
1) Catholicism made no space for the secular.
2) Any secularising force had to to oppositional to Catholicism and therefore hostile.
3) Calvinism allowed a secular space.
4) Protestantism was able to blur the distinction between the secular and sacred, integrating the two in a way that Catholicism was never able.
As John Witte shows in this book, Luther reassembled the dualism of the Augustinian two kingdoms theory in novel ways that led to relocations of the sacred, the religious and the secular. Most importantly - and this is the key difference with the laicist Southern-Latin pattern - the core dualism between the religious clergy and the secular laity is dissolved by mutual infusion, so that, in Witte's formulation, "Luther's doctrine of the priesthood of all believers at once laicised' the clergy and 'clericised' the laity."[ED] The 'clerical' office of preaching and teaching was secularised, becoming one secular vocation just like any other, while the traditional 'lay' offices now became "forms of divine calling and priestly vocation."
The 'church' is also radically transformed in the process. A new dualism now emerges between the ecclesiastical institution, which as a visible church is just, part of the saeculum that falls under the law of the earthly kingdom, i. e., the state, and the invisible church of the eschatological communion of the saints. In the process, the 'true religion', the Kingdom of God, of Love and of the Gospel, mutates into a religion of inwardness and migrates to the individual conscience, eventually giving birth to pietist movements on the margins of the ecclesiastical institution, which prepared the ground for the modern cult of the individual and the sacralisation of human rights. Secularisation or soft `deconfessionalisation' in this context means : a) continued adherence to the national church, which remains under the jurisdiction of the national sovereign; b) a drastic decline in religious (ecclesiastical) beliefs (confessional faith) and practices (rituals); c) interiorisation of a modern, individual, spiritual realm which becomes the authentic space of the sacred. There are of course tensions between the three domains of the religious-secular-sacred: a) the democratic national collective (the civil religion); b) the ecclesiastical Lutheran church; and c) the individual inward conscience. But there is no radical chasm or schism between the three.
The Southern Latin Catholic pattern evinces different dynamics of dissociation and relocation of the social sacred (state and nation), the ecclesiastical institution (the Catholic Church) and the religion of the individual. The process of absolutist confessionalisation is based on a close alliance between throne and altar, but the transnational structure of the Catholic Church and papal supremacy do not allow the kind of integration and fusion of the two one finds in the Nordic Lutheran pattern, even under caesaro-papist Gallicanism[ED]. The secularisation of the state takes place through a radical break with the church that resists disestablishment. The schism here leads to a protracted chasm, indeed to a kind of prolonged civil war within the social sacred between a new republican laicist civil religion and the old national Catholic religion. The Latin-Catholic path of laicization is marked not by integration but by civil-ecclesiastical and laic-clerical antagonism. It maintains rigidly the boundaries between the religious and the secular, but pushes those boundaries into the margins, containing, privatising and marginalising everything religious. When it breaks the monastery walls, it will not be to bring the religious into the secular world, but to laicize them, dissolving and empting their religious content and making religious people (monks and nuns) civil and laic before forcing them into the secular world. Deconfessionalisation of state, nation, and individuals here means assertive anti-Catholic unchurching.and,
The absolutist principle cuius regio ejus religio was not significantly altered by the shift of sovereignty from the monarch to the nation or people with the fall of the ancient regimes or with increasing massive democratisation process in the 20th century. European societies have remained religiously homogeneous societies, and the only significant change has been that from belief to unbelief. In this sense the process of European secularisation ought to be understood primarily as a process of deconfessionalization of states, nations, and individuals. But here one can also distinguish between the Nordic pattern of soft deconfessionalisation, which can best be characterized as 'belonging without believing', that is, secularisation without unchurching, and the more radical deconfessionalisation of the Catholic South that accompanies laicist unchurching. Denmark presents the paradigmatic case of a European society with one of the lowest rates of religious belief and practice accompanied by one of the highest rates of confessional affiliation in the national church, the Church of Denmark. In this respect, to be Danish, to be Lutheran, and to be secular amounts to one and the same thing. This contrasts with the Southern Catholic pattern (France, Belgium and, increasingly, Spain, but not so much Portugal or Italy) of radical secularization and laicist deconfessionalisation.
The secular is understood here in drastic laicist, anti-clerical, and often anti-religious terms that demand assertive unchurching. Spaniards in post-Francoist Spain who took the resisting Catholic Church to court in order to get their names erased from the church's baptismal registry may serve as a vivid illustration of this assertive deconfessionalisation.
(José Casanova:Secular and sacred? The Scandinavian case of religion in human rights, law and public sphere)