How did the kush combine Egyptian culture with parts of their own culture?

Historians often focus greatly on the empires to the north of Egypt as being the ones with whom the pharaohs had the most interaction. After all, it was the Hittites who were nearly defeated by Ramses the Great and the Assyrians and the Persians who were able to conquer Egypt. However, a powerful kingdom, named Kush, to the south of Egypt, just beyond the first rapids of the Nile, was not only able to maintain extensive economic ties with the Egyptians, but was even able to conquer them for a period of time.