This time Kush was gotten stronger then Egypt because...
Egyptianization of Kush
Several times Egypt raided Kush or took control of part of its territory. But the Kush also had accomplishment, in fact, another word for Kush is Nubia, which comes from nub, the Egyptian word for gold. Kush's location and natural resources made it an important trading hub, or center.
Kush Conquers Egypt
Kush people got back them control from Egypt so next Kush people control Egyptian. Egypt's New Kingdom collapsed so after this, Kush regained its independence. Kushites armies invaded Egypt and the kings in northern Egypt surrendered to Kush's King Piye.
Kush Capital of Meroe
About 590 B.C.E., Egypt invaded Kush and destroyed its capital city, Napata. Meroë's location helped Kush remain an important center of trade. Meroë was a large and wealthy city and it became the center of a Kushite civilization that lasted for nearly 1,000 years.
Kush Returns to Its African Roots
After splitting away from Egypt, Kush returned to its African root that are artwork, clothing, buildings and they wrote and spoke a native language called Meroitic. Kush had defeated the most powerful empire in the Roma.