In my post Why the gods will never be defeated I made many references to the rise in religiosity concomitant with modernization in South Korean. Here is an article which illustrates what I’m talking about:
As recently as 1964, only a little over 3.5 million South Koreans, out of a total population of almost 28.2 million, noted a religious affiliation on government census forms. In other words, less than four decades ago, only a little more than 12% of the South Korean people declared themselves to be Buddhist, Catholic, Protestant, or a follower of one of Korea’s many other organized religions. By 1983 more than 15.5 million South Koreans, close to 40% of a population of over 39.6 million, responded in the affirmative when their government asked them if they professed faith in any particular religion. That was more than a four-fold increase over the number of believers two decades earlier. By the 1990s, those willing to identify themselves as members of a specific religious community had risen to between 47 (in 1997) to 54 (in 1991) percent of the total population of South Korea. The size of the self-proclaimed religious population had risen from less than 16 million to between 21 to 23 million in a little more than a decade. Moreover, according to the 1997 Gallup poll, almost half of those who said they had no religious affiliation at that time confessed that they had once considered themselves Buddhists, Catholics, or Protestants….
Elsewhere you will note that the article suggests that religious affiliation is correlated both with urbanization & education. South Korea might very well be sui generis, the importance of Christianity is due both to the fact that during Japanese rule that religion was a vehicle of national resistance against colonial oppressors (who were generally Buddhist/Shinto), and, the close ties with the United States, a Christianity nation, after World War II (South Koreans also circumcise in imitation of American practices). The association of urbanization and education with religious affiliation, and in particular Christianity, seems reminiscent of the transition from godly city to pagan countryside during late antiquity. But with regards to South Korea is not the general explanatory power that is important to keep in mind, but the reminder it offers about the importance of particular & local contingent conditions. This is not to negate the power of macro forces, both historical & social, but to reiterate that sometimes the deviation around the central tendency is often only marginally less important than the modal phenomenon.
Note: Also, if you read the original article you will note that religious affiliation growth seems to have leveled off in the 1990s. This suggests that rates of growth are not constant as the innumerable parameters influencing are start to change dynamically. A simple explanation may simply be that only a subset (around 1/2) of South Koreans are naturally inclined toward religious affiliation in any case. The large number of “ex” members of various faiths and persistent between group conversion attests to the likelihood of meta-stability in this case.