What was the difference between Jazz in the 1920s and before?

I would like to know what was special about the Jazz in 1920s (Jazz Age) and how it was different from the Jazz music before then. What was special about instrumentation, rhythm and form, which made it different from before? Also, I would also like a link about Jazz history and how Jazz evolved. (Example is that Jazz in the 1930s is known as the Swing Era, so what changed when Jazz went into the 1930s)|||There's not much difference between jazz of the '20s and jazz before, because jazz as it's known today had only been in existence for about ten years at the time.