The blues draws its influences from African music, much of which was transported to the United States as part of the transatlantic slave trade. African-American slaves continued the musical traditions of their home nations and, over the generations, these musical styles became intertwined as new instrumentation and thematic content was added. Field songs and Christian gospel music also played an important part in the development of the blues as a distinct genre.
The term "blues" was coined in the 1910s to refer to the earliest publications of blues music. It implies a sadness that is common among early blues compositions.
While blues music exists in several variations, it is most commonly defined as using a 12-bar structure in which three groupings of four notes establish a specific tonality for the song. The blues notes that define the melody of a blues composition are the flat versions of the 3rd, 5th and 7th notes on the song's major scale. Specific rhythmic patterns also identify a song as in the blues tradition.
Blues music contains lyrical content that centers around several recurring themes. Besides the general sadness that the term "the blues" has come to represent, blues music often deals with issues of death, lost love, infidelity, the oppression of workers or natural disaster. These subjects owe their roots in large part to the development of the blues by African Americans; first slaves, then freed slaves who remained in the South as an impoverished agricultural workforce. Many early blues musicians were themselves sharecroppers. Others were from sharecropping communities but found time to devote to music only due to some disability that prevented them from performing manual labor, such as blindness.
Blues music developed just as the recording industry was establishing itself in the United States. Early blues records were among the most popular offerings and brought the music of isolated, rural musicians to a broad national audience.
Following World War II, the blues spread from its site of inception (the Mississippi delta region) to other parts of the country including newly emergent urban centers like Kansas City, Memphis and Chicago. There, musicians developed styles different from those of their Delta Blues forebears. The introduction of new instrumentation, notably the electric guitar and bass, gave blues musicians new means of expressing much the same themes as the earliest blues performers. As rock n' roll gained prominence, it borrowed from and further influenced the development of the blues.
Many of the earliest blues performers recorded very little, if at all. Throughout the 1960s and 1970s, music scholars frequently attempted to track down and record the music of Southern bluesmen before they were entirely forgotten to history.
Among the early blues musicians to find a lasting legacy are Robert Johnson, Blind Lemon Jefferson, Tampa Red and Lonnie Johnson.
As blues music opened itself to new styles in the post-war era, performers like Muddy Waters, Bo Diddley, John Lee Hooker and B.B. King rose to prominence. Chuck Berry was instrumental at bridging the gap between the blues and rock n' roll, and Elvis Presley became one of the first white performers to popularize a new form of blues. In the late 20th century, blues continued to have an impact on pop and rock styles as evidenced by the fusion music of Eric Clapton and Stevie Ray Vaughan.