Which factor was most instrumental in leading to the rise of the Egyptian civilization

Explanation: The most decisive factor to lead to the rise of Egyptian civilization was the unification of its cities, since with the grouping of these settlements, whose bases were the Nile Valley, the resources of the Nile River were maximized, which was considered source of economic, cultural and social development of this important civilization.

Egypt started developing after 5,500 BCE. This was a dynamic time in the Mediterranean, with Basque-Berbers sailing to that's islands, southern Greece, and the Azores. The Mediterranean flooded the Pontic basin with salt water, causing Indo-Europeans to emigrate in every direction - and even to Stonehenge. The Sahara finally dried up enough (after abundant Ice Age rain ended as Europe's glaciers retreated) to force Hamites there to emigrate into the Nile Valley. Indo-European lore referred to this as the "Flood" and to a mythic figure known both amongst German tribes and Aryans as "Manu". They passed this onto the Sumerians who passed it onto the Semites. From them through the Bible, the northerners received the "Garden of Eden", which recorded Sahara's drought, the product of an "angel with a fiery sword". Myth isn't just B. S. but an often scrambled record of the past from collective memories. It is how these ancients preserved them.