Blues is about tradition and personal expression. At its core, the blues has remained the same since its inception. Most blues feature simple, usually three-chord, progressions and have simple structures that are open to endless improvisations, both lyrical and musical.
The blues grew out of African spirituals and worksongs. In the late 1800s, southern African-Americans passed the songs down orally, and they collided with American folk and country from the Appalachians. New hybrids appeared by each region, but all of the recorded blues from the early 1900s are distinguished by simple, rural acoustic guitars and pianos.
After World War II, the blues began to fragment, with some musicians holding on to acoustic traditions and others taking it to jazzier territory. However, most bluesmen followed Muddy Waters' lead and played the blues on electric instruments. From that point on, the blues continued to develop in new directions — particularly on electric instruments — or it has been preserved as an acoustic tradition.