How did African kings from Kush conquer Egypt?

How did African kings from Kush conquer Egypt and become Pharaohs?
In the 8th century BCE, Egypt was shattered into 10 rival kingdoms. From the south, the Kingdom of Kush — centered at Napata and known as Ta-Seti, Land of the Bow — saw its chance. King Piye led 20,000 archers down the Nile, besieged Thebes and Memphis, and crowned himself Pharaoh, founding Egypt's 25th Dynasty — the era of the BLACK PHARAOHS.
This is the full story of how the Kushites didn't destroy Egypt — they restored it.