I don't mean to be offensive at all to this post, and I am sorry if I do sound offensive, but I have been having several arguments with my classmates who claim that not all black people in USA right now are from Africa. What I commonly respond to them is that I think all of them came from Africa, because of the slave trade, but when I ask whether they have/know any evidence of black people living in the Americas before the Transatlantic Slave Trade, they just say that "they just know that there was." All I'm really interested is whether we have any historical evidence that maybe black people have lived in Americas before it, or that maybe Africans, much like the vikings, have reached the Americas way before Columbus did.
More than likely, they are getting their information indirectly from the work of Ivan Van Sertima, who is pretty famous for advancing theories that Egyptians, Arabs, and Malians all crossed the Atlantic and interacted with South America and Mesoamerica at various times between 1200 BC and 1400 AD.
Van Sertima's most infamous claim is that black Egyptians were responsible for the origins of the Olmec civilization. /u/CommodoreCoco wrote an extensive post pointing out holes in that theory. I recommend you click through the first link to the Current Anthropology article "Robbing Native American Cultures" which provides even greater detail in debunking specific claims.
Van Sertima and others also popularized the claim that the Malian emperor Abu Bakri II abdicated the throne in 1312 and outfitted a fleet to explore the Atlantic, eventually reaching the Americas. The first half of that claim actually originates in near-contemporary written work by Shihab al-Umari from the 1340s, which quotes a supposed statement made 20 years earlier by Mansa Musa, saying that Abu Bakr II abdicated to explore the Atlantic and was never heard from again. From al-Umari's story, Van Sertima and other Afrocentrist writers have gone on to speculate that Abu Bakr's expedition was successful and reached the Americas.
The response of mainstream Africanist and Mesoamerican scholars has been to dismiss these claims. /u/khosikulu provides a few salient points in this post that again point holes in the Malian colonies narrative. Montellano, Haslip-Viera, and Barbour (authors of "Robbing Native American Cultures") also wrote a second article "They were NOT here before Columbus" where they asses Van Sertima's evidence for claiming Malian or Libyan contact in the new world:
Van Sertima (1992a: 22, 23; 1992b: 51; 1995: 91, 95) suggests that West Africans from Mali or southern Libya came to the Amercas before Columbus on the basis of a supposed inscription that was found on St. John in the Virgin Islands, which Barry Fell has translated and identified as Libyan script.Barry Fell is a notorious hyperdiffusionaist and retired professor of biology who claims that Celts, Egyptians, Libyans, Greeks, Phoenecians and Hebrews visited and settled in different parts of North America in antiquity (Fritze 1993: 87-89). Earlier, Fell (1975: IX) had claimed that an inscription found in caves in New Guinea and dated to 19 November 232 B.C. told of a "Libyan-Maori naval squadron which was sent to that island by the Greco-Egyptian king, Ptolemy III" (Williams 1991: 271). When it comes to Fell's analysis of inscriptions, there is hardly a scratch on a stone that cannot be translated into some ancient or medieval language that was introduced by alleged visitors from some distant region....Thus, Van Sertima is relying on very weak evidence indeed when he bases his arguments on the work of an individual such as Fell.
So, to step back from narrow critiques of Van Sertima, and address the wider question. So far, there is not any linguistic, botanical, or artifact evidence that shows Africans in the Americas before Columbus. It is theoretically possible (though seemingly unlikely) that a body of evidence might emerge which indisputably shows the presence of African peoples in the Americas prior to Columbus. However, after more than a century of linguistic, archaeological and anthropological inquiry, the weight of evidence supports the view that Africans reach the Americas after 1500, due to the Atlantic Slave Trade.
What I commonly respond to them is that I think all of them came from Africa, because of the slave trade
There are also migrants to the United States who arrived from Africa after 1865. Especially Africans who have migrated in the 20th century.