World music is often traditional indigenous local music from around the world, which has been marketed to us as world music; in other words it is music of non anglo-american language, it is music that doesn't fit into any of the other categories.
The cultural imperialist theory discusses the idea that multinational companies will 'buy up' many of these small indigenous musicians in an attempt to continue their monopoly on the sector. It could be said that world music has emerged because of this monopolisation.