Short answers, pulled from the story.
Nubia is a region along the Nile River stretching from the confluence of the Blue and White Niles near Khartoum in central Sudan to the First Cataract south of Aswan in southern Egypt. Today the region is divided between Egypt and Sudan.
Nubia conquered Egypt in the eighth century BC under Piye, ruling as Egypt's 25th Dynasty. Piye recorded his victory in a hieroglyphic stele known as the Stele of Victory and revived pyramid construction at the royal burial site of El-Kurru.
The Kingdom of Kush was the most prominent empire based in Nubia, centered first at Kerma and later at Napata and Meroe. After being pushed south by the Assyrians around 590 BC, the Kushite kingdom survived for another nine hundred years, eventually collapsing around 350 AD following an invasion by the Kingdom of Aksum.
Kandake Amanirenas was a queen of Kush who, in 25 BC, led an army that attacked the city of Syene, known today as Aswan, within Roman territory. The Roman geographer Strabo reported her forces numbered thirty thousand men. After the Romans destroyed Napata in retaliation, she continued fighting, and a peace treaty was eventually negotiated on favorable terms for Kush.
The three Christian kingdoms were Nobatia, with its capital at Pachoras (modern Faras, Egypt); Makuria, with its capital at Old Dongola; and Alodia, with its capital at Soba. They emerged around 350 AD after the collapse of the Meroitic kingdom and endured for roughly a millennium.
The Baqt was a treaty between the Christian kingdom of Makuria and the Muslim rulers of Egypt, agreed after Makuria halted the southward expansion of Islam. It required Nubians to make annual payments of slaves and other goods to the Islamic governor at Aswan and guaranteed that runaway slaves would be returned to Nubia. The treaty was kept for six hundred years.