In this article, the authors develop a theory of religious change based on the linked ecological understanding of the state-building process, to tackle the question of why the diverged path of religious change took place in South Korea and Taiwan in the 1970s. Specifically, this article aims to explain three related puzzles: (1) Given the fact that the growth of Christianity in Taiwan and South Korea was similar in the 1950s, why, in the late 1960s, did Christianity begin to grow explosively in South Korea while it stagnated in Taiwan? (2) Why did this explosive growth in South Korea occur during the Park Chung Hee regime? (3) Why did other religions (e.g., Buddhism) also grow rapidly in South Korea during the same period? Using several original materials, the authors demonstrate the central role of different statebuilding processes in sparking the diverged religious change in these two societies.