Dating back to at least 2,000 BC, the history of Nubia is confusing because several ancient kingdoms rose and fell in this part of Africa and the term "Nubia" is sometimes used to refer to one or more of these early kingdoms while at other times it just refers to the region as a whole. Complicating matters even more, the ancient Egyptians referred to their Nubian neighbors as Kushites, a kingdom in Nubia, and some sources use the term "Kush" to refer to the entire area.
The Nubian people were apparently descendants of the "the Noba people, nomads who settled the area in the 4th century [BC] following the collapse of the kingdom of Meroë," a city located on the east bank of the Nile, (Wikipedia).
The most well-known civilization of the Nubians was the previously mentioned Kingdom of Kush, which came into existence after the Bronze Age collapse (~1200 - 1150 BC) and fall of the Egyptian New Kingdom (~11th century BC). This is another source of confusion -- for me -- because at least one source I've found says that the Nubians didn't take over the region until after the fall of the Kingdom of Kush. Most of the sources, however, say that it was a Nubian kingdom, so I'll leave it at that.
Egypt had a complex and volatile relationship with Nubia. During the Early Dynastic Period (c3100 - 2686? BC), Egypt traded with Nubia, but "none of these trading expeditions, it seems, was aggressive in character, though the Egyptians occasionally had cause to protect themselves against the local populations," according to The Penguin Encyclopedia of Ancient Civilizations. During the Old Kingdom (c2613 - 2160 BC), Egyptian expeditions "were regularly sent through Nubia to obtain exotic products such as incense, ivory and panther skins. These expeditions were not without incident." (Ibid)
This trade between Egypt and Nubia continued for millennia. Wars sometimes broke out and traders were sometimes killed, apparently by local tribes, during these trade expeditions, but "relations between the two peoples also show peaceful cultural interchange and cooperation, including mixed marriages," (Wikipedia). Egypt's southern borders shifted back and forth as Egyptian power waxed and waned, and over time it appears that the two populations became thoroughly mixed.
The history of the relationship between Egypt and Nubia is long and complex, with Egypt conquering Nubia several times and Nubia conquering Egypt around 760 BC. After they defeated their northern neighbor, the Nubians established the short-lived 25th Dynasty - sometimes referred to as the Nubian Dynasty or the Kushite Empire. The Black Pharaohs didn't last very long, however. They were conquered by the Assyrians around 656 BC.
Documentary from 2015.