Why was the egyptian empire able to be controlled at times by rulers from nubia?

Explanation:

Nubians controlled Egypt at the time when the Egyptian Empire grew weak. These people had rich reserves of minerals including that of gold, iron ore and copper. Moreover, the Nubian people were great archers. Initially, the Nubians had trading and at times military relations with the Egyptians but during the course of time, the relations grow more complex.

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