I guess my definition of swing is jazz that you can dance to, and that it's growth in popularity, although not it's invention,was tied to the dances that were done by young whites and blacks from 1900 or so on. I would think that before WWI young whites would have primarily known about vaudeville music, but after WWI swing became the R&R of its time, as young whites had more ability to get out to hear music and buy records. Up until the '50's it was common for young people to drop in and out of high school to earn money for the family, but I'm sure some of that went for their entertainment too. Various dance crazes came and went during this period, as with line dancing in our era, but swing kept going too, until R&R lowered the bar.
Chris
ps - there are podcasts of Ian Whitcomb's internet shows that play a lot of pre-WWII music.