Cao Dai and Hoa Hao Buddhism are frequently mentioned in the same breath, as the two great homegrown religious movements to emerge from the Mekong Delta within a single generation, Cao Dai founded in 1926, Hoa Hao in 1939, both eventually counting millions of adherents. The pairing is understandable and also, on close inspection, somewhat misleading, because the two movements are built on nearly opposite theological instincts. Cao Dai is explicitly, deliberately syncretic: its own doctrine names Buddhism, Taoism, Confucianism, Roman Catholicism and Vietnamese folk religion as component traditions to be unified under one system, complete with its own distinctive pantheon and organisational structure modelled partly on the Catholic Church it draws from. Hoa Hao makes no such synthesis. It presents itself as Buddhism reformed and simplified, not Buddhism combined with anything else.
The difference in origin is visible in the difference in practice. Cao Dai temples are visually elaborate, drawing on the ritual and hierarchical vocabulary of the traditions it unites. Hoa Hao worship is deliberately plain, centred on the home rather than an ornate temple, in keeping with its founder's early rejection of imagery altogether. Both movements nonetheless share a common historical setting, the same Mekong Delta region, the same French colonial and then wartime Vietnamese context, and a broadly similar social base among the rural population of southern Vietnam, which is likely why outside observers have so often reached for the same comparison even where the theology itself points in different directions.