<P> In 750 BC, Napata was a developed city, while Egypt was still suffering political instability . Kashta, whose name is Egyptian for "the Kushite", profited from it, and attacked Upper Egypt . His policy was pursued by his successors Piye, and Shabaka (721--707 BC), who eventually brought the whole Nile Valley under Kushitic control in the second year of his reign . Overall, the Kushite kings ruled Upper Egypt for approximately one century and the whole of Egypt for approximately 57 years, from 721 to 664 BCE . They constitute the Twenty - fifth Dynasty in Manetho's Aegyptiaca . </P> <P> The reunited Egyptian empire under the 25th dynasty was as large as it had been since the New Kingdom and ushered in a renaissance . Religion, the arts, and architecture were restored to their Old, Middle, and New Kingdom forms . Pharaohs, such as Taharqa, built or restored temples and monuments throughout the Nile, including at Memphis, Karnak, Kawa, Jebel Barkal, and elsewhere . </P> <P> Pharaoh Taharqa's reign and that of his eventual successor, his cousin Tantamani, were filled with constant conflict with the Neo-Assyrian Empire . Around 670 BC, emperor Esarhaddon (681--669 BCE) conquered Lower Egypt, but allowed local kingdoms there to exist in order to enlist them as his allies against the Kushite rulers of Upper Egypt, who had been accepted with reluctance . </P> <P> When King Ashurbanipal succeeded Esarhaddon, the Kushite king Taharqa convinced some rulers of Lower Egypt to break with Assyrians . However, Assurbanipal overpowered the coalition and deported the Egyptian leaders to his capital, Nineveh . He appointed the Libyan chief Necho, ruler of Memphis and Saïs . Necho I was the first king of the Twenty - sixth Dynasty (664--525 BC) of Egypt, which is also known as the "Saïte Dynasty". </P>

What led to the isolation of the napatan kingdom from egypt