Why Is American Music So Largely Popular Globally and Largely Influential?

I don't quite get how American music can be so influential on a global scale and how you can find practically American music being played everywhere. I read that the majority of the roots of what we call "American music" has roots in the African American community but I don't know if this is true or not. If so, could you guys and girls answer why is it rooted and what does this tell us?