Final answer:
Around 760 BCE, the Kush King Kashta extended his control to Thebes in Egypt, marking the onset of a powerful Kush dynasty. His later successors formed Egypt's Twenty-fifth Dynasty, and even after the Assyrian expulsion, they remained a significant power in Sudan.
Step-by-step explanation:
Around 760 BCE, the Kush King Kashta extended his control to Thebes in Egypt. During a period of instability and political disunity in Egypt, Kashta took the opportunity to assert Kush dominance. This event marked the beginning of a powerful Kush dynasty and eventually led to the establishment of the Twenty-fifth Dynasty when his successor, Piankhi, gained complete control of the Egyptian Nile valley by around 716 BCE. Under the reign of Kashta's successors, namely Piankhi, Shabaqo, Taharqo, and Tamwetamani, the Nubian rulers were recognized as the legitimate sovereigns of Egypt. Their kingdom flourished for a further thousand years even after their expulsion from Egypt by the Assyrians, with Napata as their religious and cultural center.