The speed of Korean Christian growth invites explanation, and several converge. Christianity arrived without a colonial sponsor: the occupying power was Japan, not a Christian empire, so the churches could be nationalist rather than foreign, and Protestant leaders were prominent in the independence declaration of 1919. Missionaries adopted the Nevius method, which made congregations self supporting, self governing and self propagating from the outset, and translated scripture into the vernacular Hangul script at a time when the elite still wrote in classical Chinese, which tied literacy to the church.
The disruption of the Korean War, mass migration to the cities and rapid industrialisation dissolved the village and lineage structures that Confucian practice depended on, and urban churches supplied community to arriving migrants. The result includes some of the largest congregations in the world, Yoido Full Gospel Church among them, and a Korean missionary force second in size only to that of the United States. Growth has now stopped. Protestant numbers have plateaued and church credibility has been damaged by disputes over hereditary succession in large churches, by financial scandals, and by the visibility of a politically aggressive conservative Protestantism. Catholicism, associated in public memory with the democracy movement of the 1970s and 1980s, has held its reputation better while remaining smaller.