The music of America has taken over the world. There is no other music that has done that unless you want to count British bands who all--without exception--copied American music.

///The vast majority of American folk songs and ballads have British Island roots////

I'm not in agreement with that. The BEST KNOWN American folk has roots in the UK because white Americans had a tendency to only listen to the white man's music (remember, play what you know). But America has a huge French infusion that gave us Creole and Cajun music and, ultimately, jazz. Stuff like Zydeco has a multitude of influences--probably none of them from the UK. There's American Indian music, there's Mexican music. Norteno polka alone probably outnumbers all the UK-influenced stuff in America. You just don't hear about it as much. Then there's bossa nova and MPB that certainly has a huge influence (remember America isn't limited to the U.S. but Latin music even within the US is a huge business). And I won't even bring up ragtime, blues and gospel. Nowhere else on earth does such a diverse mixture of cultures exist. Too bad the music of Asia hasn't been assimilated to any real depth but I have hopes that this will happen because Asians are the fast growing populating in America. American folk is rich and it is deep. Nothing else can match it.