If you’re interested in going back as far as the early 1900’s, there was something in New York called Tin Pan Alley. That was basically office buildings with a bunch of individual small rooms with pianos. Singers for hire would sing composers’ sheet music to people who wanted to buy it. Irving Berlin, the Gershwins, George M Cohan and many others got their start that way. If your music became popular, eventually you might get a musical on Broadway. It was good practice for composers of the day to hone their talents.
By the 1920s-30s, people liked to listen to dance music at colleges or ballrooms and they would dance. Those “big bands” started off with a few seminal early groups, like Red Nichols and His Five Pennies. Nichols had some musicians who later went out and formed their own bands. Glenn Miller, Jimmy Dorsey, Jack Teagarden, Gene Krupa, Benny Goodman. All these guys later had their own big bands and were huge stars themselves. Benny Goodman, a Jew who liked black jazz and boogie woogie, became a very famous bandleader. In those days, both blacks and Jews were discriminated against, so the New York poor Jewish musicians and composers that started in places like Tin Pan Alley had a lot of empathy for the black Southerner musicians’ problems with segregation on the road. One of Goodman's musicians who went on to start his own band was Harry James. He became very successful.
Bandleader Harry James hired a little known “boy singer,” for his band, Frank Sinatra. Then Sinatra went to Tommy Dorsey’s band. And the rest is history. Other big band singers included Doris Day and many others that eventually made it in Hollywood as actors or as soloists.
Goodman and other Jewish bandleaders hired black jazz musicians to perform their swing compositions, and stuck up for them in the road. Goodman was a famous perfectionist and not everyone could keep up with him. He hired the best black session musicians he could find for his band, without concern for their color, and was notoriously strict, but fair. A lot of his musicians later had their own bands. Lionel Hampton, Gene Krupa. Glenn Miller. Swing was originally a blend of black Dixieland jazz, boogie-woogie, scat, soul music and the blues. Most of which were founded or refined by the great Louis Armstrong. He’s been described as the American Beethoven.
White Jewish musicians came along and did some great compositions and arrangements in this style. In those days black bands like Duke Ellington founded the music, but didn’t always get to play the most visible or high-paying gigs. Whites and blacks together made swing what it was. Swing morphed into early rockabilly, which led to rock and roll. All music forms with black American roots.
A lot of early twentieth century music, into the fifties, was influenced by segregation and the civil rights movement. It’s an undercurrent behind a lot of songs.
Sinatra was influenced by Goodman's integration policy and practiced it himself when he became a big star. Here’s early Sinatra, singing “I’ll Never Smile Again” with the Tommy Dorsey Orchestra.
