Muism has been the low-status stratum of Korean religion for most of recorded Korean history, and it has outlasted everything brought in above it.
Under the Joseon dynasty from 1392, Confucian officials treated mudang as improper and socially base. They were assigned outcaste status, taxed, at times expelled from the capital, and their rites classed as licentious cult, while at the same time being called on privately by court and yangban households, which is the persistent pattern in Korean attitudes toward them. Buddhism, itself under Confucian pressure, absorbed a good deal of the material instead, which is why mountain spirit shrines stand in temple grounds today.
Twentieth-century pressure came from three directions. Japanese colonial authorities regulated and policed the practice. Protestant and Catholic Christianity, growing very rapidly in South Korea, identified it as idolatry and demon worship, and Christian activists have destroyed shrines and images in incidents that continue into the present. And the Saemaul Undong from 1970, Park Chung-hee's rural modernisation campaign, targeted mudang directly as feudal superstition obstructing development, with village-level enforcement, propaganda and the removal of shrine trees and ritual sites.
The reversal is one of the more striking turns in modern Korean cultural policy. From the 1960s onward, under the cultural properties system, particular regional gut were designated as Important Intangible Cultural Heritage and named practitioners as holders, giving state stipends and protection to the same practices other arms of the state were suppressing. The reframing was as folk art and performance rather than as religion, which preserved the form while sidestepping the question of belief, and academic study by folklorists ran in parallel.
Practice today is substantial and largely urban. Estimates of the number of working mudang in South Korea run into the tens of thousands, though there is no register and the figures are soft; shamanic consultation, divination and fortune-telling are an ordinary part of South Korean life, used by people who also attend a church or a temple. Muism is also claimed as a native Korean tradition in nationalist and feminist scholarship, and appears steadily in Korean film, television and contemporary art.