In beginning of the 1940s, big-band jazz music dominated the record charts. This changed in 1942 when musicians staged a strike against large recording companies in a dispute over royalty payments. As a result, big bands began to diminish in favor of soloists or smaller groups who used guitars and vocals. The outbreak of World War II accelerated this decline, since many musicians became involved in the war effort and bands thus became smaller.
During the same period of the 1940s, African Americans emigrated in large numbers from the rural south to the cities of the north, in part to escape prejudicial laws but also to look for work in the industrial cities. They brought their music with them, which included blues, gospel, R&B, boogie-woogie and other music that influenced the development of rock 'n' roll. The emigration helped such music spread and gain followers who might not otherwise have been exposed to it. It also elevated African-American culture as a vital part of America: there was a push for greater rights for minorities and further integration into society.
Musician Les Paul further added to rock 'n' roll's prominence with the creation of the electric guitar in the early 1950s. (He also invented eight-track recording.) That gave rock 'n' roll its signature instrument, but other technological innovations helped spread it further. America had become a car-obsessed culture in the 1950s, with car radios spreading the impact of the new form of music. And television broadcast the music as well - notably the "Bandstand" TV show (which later became "American Bandstand") showcased new musical talents. Many of "Bandstand"'s early performers were white, exacerbating the racial tensions which rock 'n' roll attempted to straddle.
The spread of rock 'n' roll records brought about a new sense of freedom, with lyrics that were often sexually suggestive. Many musicians themselves lived wild lives that included drugs and alcohol use. This caused a great deal of controversy as conservative elements of society thought that rock 'n' roll was "corrupting" American society. However, the freedom associated with rock 'n' roll gave a new sense of identity and voice to those who listened to it. As the listeners came of age, that voice exploded into calls for social justice, protests against the Vietnam War and calls for greater openness and tolerance in American culture.