I think the collision/interaction/synthesis of European and African musical conceptions that occurred in the Western Hemisphere during the 14th through 19th centuries marked the creation of a new "genre," and eventually a whole slew of genres. Certainly the most important musical genre in history, and in at least that one sense, the "greatest."

Indeed, that synthesis is the basis of just about every different kind of music we enjoy today, with just a few obvious exceptions: pre-existing stuff like pre-1492 European classical compositions, Gregorian chant, and the long-established musical traditions of India, China, Japan and other Asian cultures. And, of course, the folksong traditions of the various European peoples.

Folks can argue whether the very first interplay of African and European music took the form of blues or spirituals or early-jazz or whatever ~ my vote is for "work songs" ~ but all the plausible suggestions fall under the umbrella category of American Folk Music.