
In the early 1940s in jazz, bebop emerged, led by Charlie Parker, Dizzy Gillespie, Thelonious Monk and others. It helped to shift jazz from danceable popular music towards a more challenging "musician's music." Differing greatly from swing, early bebop divorced itself from dance music, establishing itself more as an art form but lessening its potential popular and commercial value. The swing era lasted until the mid-1940s, and produced popular tunes such as Duke Ellington's "Cotton Tail" (1940) and Billy Strayhorn's "Take the 'A' Train" (1941). When the big bands struggled to keep going during World War II, a shift was happening in jazz in favor of smaller groups. Some swing era musicians, like Louis Jordan, later found popularity in a new kind of music, called "rhythm and blues", that would evolve into rock and roll in the 1950s.