Phở or pho is a Vietnamese soup consisting of broth, rice noodles called bánh phở, a few herbs, and meat, primarily made with either beef or chicken. Pho is a popular street food in Vietnam and the specialty of a number of restaurant chains around the world. Pho originated in the early 20th century in northern Vietnam, and was popularized throughout the rest of the world by refugees after the Vietnam War. Because pho's origins are poorly documented, there is significant disagreement over the cultural influences that led to its development in Vietnam, as well as the etymology of the word itself. The Hanoi and Saigon styles of pho differ by noodle width, sweetness of broth, and choice of herbs. A related noodle soup, bún bò Huế, which is a spicy beef noodle soup, is associated with Huế in central Vietnam.