Influenced by work songs, church music and folk, Blues developed in the Southern United States. The earliest references of blues date back to 1890’s and was primarily played by the Southern black community. Blues developed in Georgia, Texas and Mississippi, where slight variations of style developed such as Mississippi Delta blues. Players such as Blind Lemon Jefferson, Charley Patton and Robert Johnson paved the way for the genre where over time cities such as Atlanta, Memphis and Chicago began to adopt the sound.
After World War II electric guitar became paramount in blues music, with musicians such as Muddy Waters, Howlin’ Wolf, Buddy Guy and many more championing the genre. The blues heavily influenced Elvis Presley and later British rock icons such as The Rolling Stones, John Mayall and Eric Clapton.
The foundation of most blues music is the 12-bar. Using a 4/4 time signature, the term 12-bar counts the number of measures. Divided into three four-bar segments. The 12-bar uses the first, fourth and fifth notes of an eight-note scale. The I chord being played for the first four bars, the IV chord in the second four bars and then the V chord and IV chord in the last four bars. Not all blues songs are in 12-Bar arrangement, but this progression will help you to understand the foundation of many blues songs. Try improvising the E minor pentatonic scale over a 12-Bar in Em (I = Em, IV - Am, V = Bm7)