Country blues

Country blues (also folk blues, rural blues, backwoods blues, or downhome blues) refers to all the acoustic, mainly guitar-driven forms of the blues. After blues' birth in the southern United States, it quickly spread throughout the country (and elsewhere), giving birth to a host of regional styles. These include Memphis, Detroit, Chicago, Texas, Piedmont, Louisiana, West Coast, Atlanta, St. Louis, East Coast, Swamp, New Orleans, Delta and Kansas City blues.

Source : http://en.wikipedia.org/wiki/Country_blues