As a footnote: I didn't quite finish the point about the soldiers mingling in the war. It was the first time most non-southerners had heard southern music, which before that was a strictly regional market.

Once the sounds got spread around, they traveled fast in the hands of people from all over the US -- and overseas, spawning country music markets wherever US forces went, Europe, the Pacific, etc.

Suddenly country sounds were no longer a well-kept secret. With so much input from so many places, the style changed very fast. You can thank the war for C&W (or blame it, as you please). Wars are famous for creating melting pots for musical styles. Writing styles too -- Hemingway and many more came out of WWI. Wars just mix everything up, they are a really hot growth medium. (That can be good in some ways...obviously horrible in others. But that's what happens.)

Bob