As George implied early in the thread, this is a huge question that's as complex as the social histories that motivated the tunes and songs in the first place. There are many contributors to this musical heritage: the composers, the collectors, the publishers, the archivists, the recording artists, and now the web community.

Above all I think you should include in your needlework the images of some faceless musicians and singers on a back porch or at a kitchen party. Collectively they have contributed more than all the others combined! ;-)