Country music is popular across the United States because a quack doctor in Kansas in the 1920s who treated impotent men by surgically implanting goat testicles into their scrotum lost his medical license, so he ran for Governor of Kansas because that job would let him assign new members to the state medical board who would reinstate his license, and he only lost because the Republican and Democratic parties changed the election rules to throw out any votes for him that didn't write in his full name in a single approved way, so he moved to Texas and set up a million-watt radio station across the Mexican border that let him blast quack medical advice and sales pitches for patent medicines across the entire continent, and he needed something to fill airtime when he wasn't on selling joy juice, so he filled it with country music
Someone turned the story of John R. Brinkley into an animated documentary a few years back. It's rated 94% Fresh on Rotten Tomatoes. You can stream it on most online rental services for around $4*.
(* In the US, pricing and availability may be different elsewhere)