Cao Dai has spent almost its entire existence in a difficult relationship with whoever held power in Vietnam.
The French read it as a nationalist movement in religious form and exiled its leadership. The Japanese armed it. Through the First Indochina War it functioned as an autonomous power around Tay Ninh with its own army, and in 1955 and 1956 Ngo Dinh Diem dismantled that position by force. After 1975 the new government took over its schools, hospitals and printing works, restricted the hierarchy, and banned the spirit-writing sessions that had produced the religion's scripture in the first place. The 1997 recognition installed a state-approved governing council, and a continuing dissident current inside Vietnam and in the diaspora holds that the recognised body is not the legitimate church.
The religion is also not a single institution. The Tay Ninh Holy See is the largest and best known, but at least a dozen separate branches exist, including Ban Chinh Dao based at Ben Tre and Tien Thien, several of which broke away in the 1930s over questions of authority and doctrine.
Numbers vary with who is counting and which branches are included. Vietnamese government figures give roughly 4.4 million affiliated to Tay Ninh, and totals of up to six million once other branches are added; a United Nations figure from 2015 gave about 2.5 million. Communities of tens of thousands live in Cambodia, the United States, Australia, Canada and France. On any of these figures Cao Dai is one of the larger religions founded anywhere in the twentieth century.