After the end of the French rule in 1954s, Catholicism declined in the North, where the Communists regarded it as a reactionary force opposed to national liberation and social progress. In the South, by contrast, Catholicism was expanded under the presidency of Ngo Dinh Diem, who promoted it as an important bulwark against North Vietnam.

Diem, whose brother was Archbishop Ngo Dinh Thuc, gave extra rights to the Catholic Church, dedicated the nation to the Virgin Mary and preferentially promoted Catholic military officers and public servants while restricting Buddhism and allowing Catholic paramilitaries to demolish temples and pagodas.

In 1955 approximately 600,000 Catholics remained in the North after an estimated 650,000 had fled to the South in Operation Passage to Freedom.