During the time of the middle kingdom and the new kingdom, why did egypt conquer most of kush?

The Tenth Dynasty ruled northern Egypt, while the Eleventh Dynasty ruled the south. Around 2000 BC, a powerful leader named Mentuhotep II became king of southern Egypt. He launched an attack on the north and eventually reunited Egypt under one rule. This began the period of the Middle Kingdom.

answer; eliminate parking problems in cities, because a car took up only half as much space as a horse and buggy;