In my opinion, as Jazz become one of the famous type of music, so knowing the history of Jazz is very necessary. Jazz music is very difficult to define mainly because there are so many different styles. When considering Ragtime, Stride and Boogie Woogie, these three styles was very essential in the development of modern jazz. However, the most essential that built Jazz in back then should be Ragtime, so I agree with you. In addition, Ragtime is primarily an African American invention and was a source of pride to African American composers, musicians, and listeners. Ragtime really isn 't jazz since it rarely includes improvisation. However, it was the immediate precursor of jazz ("What is"). It is often referred to as the founding style of jazz.