How did the Egyptians develop a complex civilization in North Africa?
For Egypt, geography and topography were vital in allowing civilization to develop.
In terms of geography, the Nile was the major factor. The Nile flooded at regular intervals and in relatively gentle ways. This created a great deal of fertile land in the Nile Valley. This land could be farmed and formed the basis of the Egyptian civilization.
Topography allowed the civilization to grow without much outside interference. Deserts, the ocean, and the rapids and waterfalls of the Nile made invasions very difficult. This allowed the civilization to grow and become more complex.