It was called hillbilly music, and it was commonly played by and
listened to by poor white rural folks. It was changed to "Country and
Western" to be less offensive, because "hillbilly" can be taken as an
offensive term. Since country music artists were incorporating western
themes into their music, they combined the terms "Country and Western"
as one genre.

The same goes for blues music and related music styles. It was known
as "Race" music, used for poor black musicians, but they changed it to
"Rhythm and Blues" to be less offensive.

I would be considered a "hillbilly", because to me, "hillbilly" means
a rural person who lives in the hills. But, most people call me a
"hillbilly" to insult me.