During the struggle for independence from the French, the song “Thanh niên Hành Khúc” (Call to the Youth) was used as the unofficial anthem of the Provisional Central Government of Vietnam. The original lyrics were written by Lưu Hữu Phước, who was a student during World War Two, his anthem caught on with other students. The Provisional Central Government became the government of South Vietnam after the 1954 Geneva Accord split Vietnam into North and South entities, and after independence in 1955, the lyrics were revised by the first president of South Vietnam, Ngô Đình Diệm, who made the lyrics more inclusive of the entire population, not just youth.
Lưu Hữu Phước wrote the lyrics in what was later North Vietnam; he later became a communist and fought against the South Vietnamese government. He wrote many communist patriotic songs, including the anthem adopted by South Vietnam after the control of the country’s government fell to the communists.
Presently, the anthem is used both by the South Vietnamese diaspora in the United States and around the world as the “Anthem of Free Vietnam”, and the original lyrics are also sung in communist Vietnam itself as a revolutionary song, despite the fact that the melody was used as the anthem of democratic South Vietnam.
Special thanks to: Ben Cahoon, Quang Hong, Le Phan Huu Bang, and Huynh Ba Thanh for some of this information.