The Cult of Amun
In its 3,000-year history as a state, ancient Egypt had a complicated, constantly changing set of relations with neighboring powers. With the Libyans to the west and the Babylonians, Hittites, Assyrians, and Persians to the northeast, Egypt by turns waged war, forged treaties, and engaged in mutually beneficial trade. But Egypts most important and enduring relationship was, arguably, with its neighbor to the south, Nubia, which occupied a region that is now in Sudan. The two cultures were connected by the Nile River, whose annual flooding made civilization possible in an otherwise harsh desert environment. Through their shared history, Egyptians and Nubians also came to worship the same chief god, Amun, who was closely allied with kingship and played an important role as the two civilizations vied for supremacy.
During its Middle and New Kingdoms, which spanned the second millennium B.C., Egypt pushed its way into Nubia, ultimately conquering and making it a colonial province. The Egyptians were drawn by the lands rich store of natural resources, including ebony, ivory, animal skins, and, most importantly, gold. As they expanded their control of Nubia, the Egyptians built a number of temples to Amun, the largest of which stood at the foot of a holy mountain called Jebel Barkal. This the Egyptians declared to be the gods southern home, thereby conceptualizing Egypt and Nubia as a unified whole and justifying their rule of both. After Egypts New Kingdom collapsed around 1069 B.C., the kingdom of Kush rose in Nubia, with its court based in Napata, the town adjacent to Jebel Barkal. The Egyptian colonizers may have been gone, but their religious legacy lived on, as the Kushite rulers were by this time fervently devoted to Amun. Just as the Egyptians had used the god to validate their conquest of Nubia, the Kushites now returned the favor. During a period of discord in Egypt, the Kushite king Piye first secured Amuns northern home, in Karnak, Egypt. Then, claiming to act on the gods behalf to restore unified control of Nubia and Egypt, he conquered the rest of Egypt and, in 728 B.C., became the first in a line of Kushite pharaohs who ruled Egypt for around 70 years.
http://www.archaeology.org/issues/174-1505/features/3146-sudan-nubia-dangeil-cult-of-amun-ra#art_page4