Most forms of American music can trance their roots back to The Blues, a music that was invented by African-American slaves living in the southern states of the United States. In his autobiography, former slave Frederick Douglass writes about the music made by a people living under a horrifying system of forced labor:

"I have often been utterly astonished, since I came to the north, to find persons who could speak of the singing, among slaves, as evidence of their contentment and happiness. It is impossible to conceive of a greater mistake. Slaves sing most when they are most unhappy. The songs of the slave represent the sorrows of his heart; and he is relieved by them, only as an aching heart is relieved by its tears. At least, such is my experience. I have often sung to drown my sorrow, but seldom to express my happiness. Crying for joy, and singing for joy, were alike uncommon to me while in the jaws of slavery. The singing of a man cast away upon a desolate island might be as appropriately considered as evidence of contentment and happiness, as the singing of a slave; the songs of the one and of the other are prompted by the same emotion."

The Blues became a way for people living under slavery to cope with the incredible hardships they faced. It helped by giving a means of expression and catharsis (the process of releasing, and thereby providing relief from, strong or repressed emotions).

The Blues began as an oral tradition wasn't written down or recorded until the late 19th century and early twentieth century. The first known book that attempted to represent the music was Slave Songs, published in 1867. You can view the book here.