In the 1930s swing bands emerged at the forefront of American popular music, evolving from the jazz genre, which was primarily produced and listened to by blacks, into one patronized also by urban whites. Long before baseball was integrated, the big swing bands—led by Duke Ellington, Benny Goodman, and Count Basie—brought together black and white musicians in a new social amalgam that decisively changed American culture. Musically, swing offered rhythmic flexibility. Swing music is marked by a subtle swaying, living pulse, which came from musicians playing just ahead of the beat enough to be syncopated, or dragging behind it enough to be bluesy. Swing, notes historian Lewis Erensberg, caused "a general revolution in the popular dance in the United States" as white youth took up the black dance innovations in order to banish whatever ballroom gentility remained in the Depression. After World War II...