Perhaps before we begin to decide whether "ebonics" is a
dialect or a
slang, we should look at the
origin of ebonics.
In the beginning, black people lived in Africa. There were no black people in the Americas until the slave trade began, and in Africa, there were few, if any, strong black states. Blacks in Africa spoke thousands of languages, often wildly varying from village to village.
Now, during the age of imperialism, traders from Western Europe communicated with the natives of their colonies via simplified languages collectively known as pidgin, which mixed a European vocabulary with a nativized grammar. Many different forms of pidgin have been devised: the forms of pidgin used in West Africa and the South Pacific are the most widespread today.
After slaves were trapped, they would be sent to forts on the West African coast to be collected and shipped to the New World. They would be surrounded by people speaking a variety of different languages, and would be taught the basics of pidgin by the slave traders, learning some more on the hellish ride across the Atlantic Ocean. This would be the basis of their communication with plantation owners upon their arrival in the Americas.
"Ebonics" generally refers to the evolved form of this pidgin English spoken in the United States, but the patois of Jamaica and the Bahamas, as well as Haitian Creole, share similar origins. In fact, conversations between two Bahamians and conversations between two men on the Congo River (in West African Pidgin English) will sound very similar to each other, even today.
Ebonics, however, sounds notably different from the slave languages of the Caribbean, and there is a reason for this. In the South, whites originally spoke a British style of English, while blacks originally spoke in pidgin. However, white children were usually raised by a slave nanny, and often played with a slave playmate: these interactions during the formative stages of language acquisition meant that, over the next couple of hundred years, ebonics began to sound more like Queen's English, and the white southerners' speech began to sound... well, blacker, something they often tried their best to cover up in the circles of aristocracy. But that's another story.
Ebonics truly began its nationwide spread after the end of the Civil War, when many blacks in the South were suddenly free to move to major cities in the North and take on a new life. Soon, cities all over the country had black populations speaking ebonics, and a single ebonics dialect began to coalesce—the black English that we hear today from Atlanta to New York City to LA.
Black culture in general owes much to the many cultures of West Africa. Pentecostalism is essentially a flavor of Christianity heavily influenced by old village rituals, with the preacher man taking the place of the chief; rap and jazz are both descended from improvisational tribal music. Ebonics is only one part of this culture, but indeed an important one, as it is how the essence of the African-American community has been passed from generation to generation in the United States.