Here are the first two of Professor Alec Ryrie's four Bampton Lectures given at Oxford in 2022 (the second lecture begins at 53:38). The latter two are more about Ryrie's speculations of the future than the history of Christianity after World War 2.
You can see lectures 3 and 4 here:
Lecture 3 - https://www.youtube.com/watch?v=rnob1qOTq38
Lecture 4 -https://www.youtube.com/watch?v=uFKuoGNRnXA
Alec Ryrie is an expert in the Reformation and the history of Early Modern Europe in general. For the 2022 Bampton Lectures, he chose a far more modern subject: Hitler's eclipse of Jesus as the chief moral figure of the 20th century. This is not to say that Hitler was viewed as a moral exemplar, but rather that the rejection of Hitler formed the shared basis for moral thinking after World War 2. This new shared moral foundation in rejecting Hitler is precisely why Christian Democracy floundered after its brief moment of ascendance from 1945 to 1960. By the 1960s, the vestiges of Christian morality which were still espoused by Christian Democrats were seen as baseless and intolerable for an anti-Fascist society. Moreover, as Ryrie outlines, Christianity had been discredited by its cozy relationships with far-right regimes prior to World War 2. Hence the explosive rejection of Christian Democracy by 1968.
Ryrie mainly focuses on Protestantism after the War, and does not talk about Vatican II or the Catholic experience. Compare, however, the Protestant theologians' embrace of secularity with the attitude of hierarchs like Pope Paul VI in the 1960s, who spoke of the necessity of dispensing with tradition for the sake of embracing "modern man". Likewise these two talks might clarify what so many churchmen meant by "modern man". By the 1950s, perhaps "modern man" was the man envisioned by the United Nations and the Atlantic Charter. He is a man who values democracy, human rights, science, and a universal, secular ethic of freedom. While none of these values are necessarily bad in and of themselves, they are together constitutive of a secular "religion" that has managed to absorb Christianity (and most other religions) in the decades since World War 2.
In a 1979 interview the Eastern Orthodox theologian Alexander Schmemann thus describes this post-war approach to religion:
"I would understand Christian love as not excluding conflict. My desire for unity would be such that would like to convince you of something, and not simply have a cup of coffee together. I feel that it is this American 'civil religion' (call it what you will) on the other hand, this symbolism of union without unity, of good relations…I see people all of the sudden going into synagogues, Christians, to partake of the Passover Meal. It's quite a fad, you know. People go, exchange pulpits, we show them our vestments, they show us theirs. All this maybe is necessary for a certain balance of our society. It is a kind of American instinct to minimize tensions. I am not condemning it, but it is a great enemy of any serious discussion. This is something which satisfies us easily. We can leave in the evening saying, 'They were nice, we were nice, everything is nice.' We Christians are still, after all, good people, all of us."