In my studies it was made very clear that African Americans and Creoles were responsible for the creation of blues, rock, jazz, funk, and hip-hop, which is basically everything except for Appalachian folk music and the genres that grew out of it. It is important to note that once a genre was created whites seemed to be equally capable at contributing and evolving the genre, and in many cases (like rock and roll) took over it completely.
One explanation is that black people are just naturally better at inventing new genres. What I think is more likely however is that something about being "held back by the man" has helped certain people to create new forms of art. This theory also makes sense if you look at at the origins of the blues in the late 19th century, which basically evolved from the "field hollers" that slaves would sing to to vent their feelings as they worked.
It should also be noted that some influence would have definitely come directly from African tribal music, but I think that the possibility of this being the only cause stops after the blues as the small amount of knowledge that would have been conserved to that point would by then be out in the open.
I have a double major in music and computer science, so I have learned a fair amount about how western music (both popular and "art") got to where it is today. What I'm looking for are comparisons in markets that were not heavily influenced by western pop music.
It would also be interesting to see if similar things have happened with other forms of art besides music.
African Americans have sparked basically every new form of popular music.
There's an issue with your premise: while African-Americans and other people of color were integral to the development of different styles of music, which went on to be embraced as popular styles by the public, those styles did not arise ex nihilo, nor were they the only styles to emerge from the American melting pot. In addition to blues, rock, jazz, et al. you also have to consider waltzes, ragtime, marches, folk ballads, etc. - and you might also add gospel, exotica, various avant garde styles (like the innumerable and often idiosyncratic electronica styles), country and western, salsa, etc. Further, categorizing blues as arising from "field hollers" is both inaccurate and simplistic; black slaves in the United States brought with them certain musical traditions and techniques (such as call-and-response singing, blue notes, and forms of syncopation), which then were further developed in the cultures they found themselves in - drawing on, among other things, transplanted European traditions (like the Irish-Scotch ballad) and instruments.
I would recommend you take a look at Peter Van der Merwe's Origins of the Popular Style: The Antecedents of Twentieth-century Popular Music, which while incredibly dry, does a very good job at looking at the history and development of popular music in the United States.