The blues developed in the United States in the late 19th century from field hollers and chants sung by slaves in the Deep South to get through the day. This expression of raw emotion and suffering became a blues trademark.
The standard blues form is the 12-bar form, which consists of a three-chord harmonic progression played in a 4/4 time signature.
According to Stephen J. Nichols, author of "Getting the Blues: What Blues Music Teaches Us about Suffering and Salvation," the blues speaks truthfully to the human experience. According to blues musician Howlin' Wolf, "Blues come when you can't pay your rent...got no money."
According to PBS's multimedia project "The Blues," electrified blues was popular on American radio during the 1940s and 1950s. It was also a huge influence on rock and roll, jazz, and a number of other styles.
Blues music varies from city to city. Blacks emigrated to northern cities following the Civil War and, as a result, cities like Chicago, Memphis, and Detroit ended up producing their own unique breed of blues music.