Short answers, pulled from the story.
Buddhism may have reached Vietnam as early as the 3rd or 2nd century BCE from the Indian subcontinent, or during the 1st or 2nd century CE from China. By the end of the 2nd century CE, Luy Lau, in modern Bac Ninh Province, had become a major regional Mahayana Buddhist hub visited by Indian missionary monks traveling to China.
Estimates vary significantly by source. Vietnam's 2019 National Population and Housing Census counted approximately 4.6 million Buddhists, about 4.8% of the population. The U.S. Department of State's 2023 report cited Vietnam's White Book, which recorded approximately 14 million Buddhists in 2021, representing 13.3% of the overall population.
The Buddhist crisis began in May 1963 in Hue, when Buddhists were prohibited from displaying flags during Vesak while Catholics were permitted to fly religious flags days earlier. Troops sent to suppress protests killed nine civilians, triggering mass rallies. The crisis culminated in the self-immolation of Thich Quang Duc in protest of the persecution of Buddhists by the Diem government.
The Truc Lam school is a distinctly Vietnamese school of Zen Buddhism, founded by Emperor Tran Nhan Tong (1258-1308) after he left his royal family in 1299 to become its first ancestor. Monk Phap Loa and Monk Huyen Quang became the second and third ancestors of the school. It is syncretic, combining elements of Pure Land and Thien practices.
Le Van Giang, a veterinary doctor who encountered Theravada Buddhism while working in Phnom Penh, was among the first to bring the tradition to ethnic Vietnamese. He ordained and took the name Ho Tong (Vansarakkhita). In 1940, he helped establish the first Theravadin temple for Vietnamese Buddhists, Buu Quang, at Go Dua, Thu Duc. He was later elected the first President of the Vietnamese Theravada Buddhist Sangha Congregation in 1957.
The Communist Party of Vietnam officially promotes atheism but generally favors Buddhism, viewing it as associated with Vietnamese national history and patriotism. Buddhist festivals receive government promotion and restrictions are few compared to those placed on Christian, Muslim, and other religious communities. However, no organized sangha is permitted to operate independently of the state, and the Buddhist Sangha of Vietnam, established on the 7th of November 1981, remains the only officially recognized Buddhist body.