The Mills Brothers made musical and social history in the U.S. They brought African-American music into the segregated pop mainstream at a time when most artists of colour were kept off the radio and relegated to "race" record labels. One of the most universally successful vocal groups in the years before World War II, The Mills Brothers were conscious of their role, sweetening their blues sound just enough to win over audiences accustomed to a bland diet of schmaltzy orchestral music. Remarkably, they did all this with only four voices and an occasional guitar.