Blues is an African-American music that traverses a wide range of emotions and musical styles. "Feeling blue" is expressed in songs whose verses lament injustice or express longing for a better life and lost loves, jobs, and money. But blues is also a raucous dance music that celebrates pleasure and success. Central to the idea of blues performance is the concept that, by performing or listening to the blues, one is able to overcome sadness and lose the blues.Among the formal, identifying musical traits of the blues are the familiar "blue notes," a three-line AAB verse form, and a characteristic use of the familiar blues chord progression. Historically, the popularity of blues coincides with the rise of the commercial recording industry, the introduction of "race" records aimed at black record-buyers after 1920, and the emigration of black Americans from the rural South to the urban North. Many of the earliest black American recording stars were blues singers. The first blues songs to be recorded, often called "classic blues," were jazz-influenced songs in a vaudeville style, sung by the great blueswomen: Gertrude "Ma" Rainey, Bessie Smith, and others. These singers were often accompanied by pianists, guitarists, or even small jazz combos.The "country blues," usually considered an earlier form of the genre, was actually recorded in the mid-1920s. There are several regional styles of country blues, including delta blues from the Mississippi Delta, Texas blues, and Piedmont blues from the Southeast. Country blues was usually recorded by a single male singer, self-accompanied on the guitar or piano, with perhaps an accompanying harmonica or simple percussion. Charley Patton, Blind Lemon Jefferson, Blind Boy Fuller, and Robert Johnson were country blues musicians.Beginning in the 1930s, blues musicians fell under the influence of urban culture, including popular music and jazz. Combos incorporating piano, guitar, and percussion developed, although the country, "downhome" origins of the musicians were still evident in the music. Major musicians of the 1930s included Tampa Red, Big Bill Broonzy, Little Brother Mongomery, Leon Carr and Scrapper Blackwell, Lonnie Johnson, and Memphis Minnie.After World War II, the use of electrified instruments became inevitable. During the 1940s, some blues bands even incorporated saxophones, although the preference was for amplified harmonicas, especially in Chicago, a predominant center of blues recording in the 1950s. Blues from this period is often called "urban blues," "electric blues," or simply "Chicago blues." Important urban blues musicians included Muddy Waters, Little Walter, Elmore James, Howlin' Wolf, T-Bone Walker, and B. B. King.Blues remains with us in contemporary American culture, and as a traditional musical form it has been subjected to countless revivals and reinterpretations. Its current practitioners often integrate the sounds and instrumental pyrotechnics of rock music and the sheen of urban soul; but the twelve-bar form, variations on the blues chord progression, and emotive lyrical content remain relatively unchanged.