What secularisation theory has missed is this crucial historical fact: Christianity has not operated in a linear fashion at all. It has instead been cyclical — prospering in some places and declining in others according to a pattern that secular thinkers have neglected to explore. This includes periods of prosperity in this and the last century.

The Second World War was followed by a religious boom in every Western country. In an essay reviewing the role of religion in the British, American, and Canadian armies the British historian Michael Snape concludes that the soldiers of all three nations "were exposed to an institutional process of rechristianisation during the Second World War, a process that was widely reinforced by a deepening of religious faith at a personal level". This experience, he concludes, further reinforced "a religious revival that was stirring in the war years and which was to mark all three societies until the religious ferment of the 1960s". 

The British historian Callum G. Brown agrees. As he has put it, summarising evidence of a religious boomlet across the West in the mid-20th century, "Between 1945 and 1958 there were surges of British church membership, Sunday school enrolment, Church of England Easter Day communicants, baptisms and religious solemnisation of marriage, accompanied by immense popularity for evangelical ‘revivalist' crusades." That trend also held elsewhere in the Western world — in Australia, West Germany, France, Spain, Belgium and the Netherlands. 

As for the United States, the same postwar religiosity appears in retrospect as the high-water mark of Christianity in America. So pronounced was public religiosity and so vibrant were the churches that Will Herberg, perhaps the foremost sociologist of religion in America during the mid-20th century, could observe in his classic book Protestant-Catholic-Jew: "The village atheist is a vanishing figure . . . Indeed, their kind of anti-religion is virtually meaningless to most Americans today . . . This was not always the case; that it is the case today there can be no reasonable doubt. The pervasiveness of religious identification may safely be put down as a significant feature of the America that has emerged in the past quarter of a century [emphasis added]." In the gap between his assessment of the religiosity of his day and our assessment of its decline less than 60 years later, we see once more that Christianity ebbs and flows even in the modern world, in ways more mysterious than first understood and that point away from the conclusion that decline is inevitable.