The origins of rock and roll have been fiercely debated by commentators and historians of music. There is general agreement that it arose in the Southern United States – a region which would produce most of the major early rock and roll acts – through the meeting of various influences that embodied a merging of the African musical tradition with European instrumentation. The migration of many former slaves and their descendants to major urban centers like Memphis and north to New York City, Detroit, Chicago, Cleveland and Buffalo (See: Second Great Migration (African American)) meant that black and white residents were living in close proximity in larger numbers than ever before, and as a result heard each other's music and even began to emulate each other's fashions. Radio stations that made white and black forms of music available to both groups, the development and spread of the gramophone record, and African American musical styles such as jazz and swing which were taken up by white musicians, aided this process of "cultural collision".
The immediate roots of rock and roll lay in the rhythm and blues, then called "race music", and country music of the 1940s and 1950s. Particularly significant influences were jazz, blues, gospel, country, and folk. Commentators differ in their views of which of these forms were most important and the degree to which the new music was a re-branding of African American rhythm and blues for a white market, or a new hybrid of black and white forms.
In the 1930s jazz, and particularly swing, both in urban based dance bands and blues-influenced country swing, was among the first music to present African American sounds for a predominantly white audience. The 1940s saw the increased use of blaring horns (including saxophones), shouted lyrics and boogie woogie beats in jazz based music. During and immediately after World War II, with shortages of fuel and limitations on audiences and available personnel, large jazz bands were less economical and tended to be replaced by smaller combos, using guitars, bass and drums. In the same period, particularly on the West Coast and in the Midwest, the development of jump blues, with its guitar riffs, prominent beats and shouted lyrics, prefigured many later developments. In the documentary film Hail! Hail! Rock 'n' Roll, Keith Richards proposes that Chuck Berry developed his brand of rock and roll, by transposing the familiar two-note lead line of jump blues piano directly to the electric guitar, creating what is instantly recognizable as rock guitar. Similarly, country boogie and Chicago electric blues supplied many of the elements that would be seen as characteristic of rock and roll.