The Blues has its roots in Africa, probably from the West Africa where people, known as the Griot, played music on a sort of banjo looking instrument and sang about joy and telling stories.

When African people was brought to North America as slaves, to work in the cotton and tobacco fields in the Mississippi River Delta region, they took the singing and playing with them. They so-called work songs, 'workers' were allowed to sing songs during their working time, had hidden verses(sung when the 'master's' wasn't near/hearing them) that expressed the social misery, sadness, pain and fear about their situation. 

In the early 1900's the Blues grew out of this music story telling songs(work songs/negro spirituals), melting European musical traditions with the African music.

The 'Bluesy' style of the music, played on guitar(shifted from the banjo), a 12-bar pattern with three major chords and emotional lyrics was shaped between the 1920's and 30's.

The Blues became more widely known through the urbanization(migration of people from the countryside to the cities) of the Southern United States in the 1930's and 40's.

Blues..without the Blues there would not have been any Hard Rock.

In the 40's the recording techniques, radio broadcasting of live performances and the amplifying of the instruments was the breakthrough for the Electrified Blues.

With Bluesplayers such as  Muddy Waters,  Elmore James, John Lee Hooker and others playing the guitar distorted and at high volumes not only sets the parameters for the Electrified Blues but also for the Rock'n'Roll to come.